The Tor Browser: toolkit/content/widgets/scrollbox.xml@6474c204b198 (annotated)

toolkit/content/widgets/scrollbox.xml@6474c204b198 (annotated)

toolkit/content/widgets/scrollbox.xml

Wed, 31 Dec 2014 06:09:35 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 06:09:35 +0100
changeset 0: 6474c204b198
permissions: -rw-r--r--

Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

 <?xml version="1.0"?>
 <!-- This Source Code Form is subject to the terms of the Mozilla Public
    - License, v. 2.0. If a copy of the MPL was not distributed with this
    - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
 <bindings id="arrowscrollboxBindings"
    xmlns="http://www.mozilla.org/xbl"
    xmlns:xul="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
    xmlns:xbl="http://www.mozilla.org/xbl">
   <binding id="scrollbox-base" extends="chrome://global/content/bindings/general.xml#basecontrol">
     <resources>
       <stylesheet src="chrome://global/skin/scrollbox.css"/>
     </resources>
   </binding>
   <binding id="scrollbox" extends="chrome://global/content/bindings/scrollbox.xml#scrollbox-base">
     <content>
       <xul:box class="box-inherit scrollbox-innerbox" xbl:inherits="orient,align,pack,dir" flex="1">
         <children/>
       </xul:box>
     </content>
   </binding>
   <binding id="arrowscrollbox" extends="chrome://global/content/bindings/scrollbox.xml#scrollbox-base">
     <content>
       <xul:autorepeatbutton class="autorepeatbutton-up"
                             anonid="scrollbutton-up"
                             collapsed="true"
                             xbl:inherits="orient"
                             oncommand="_autorepeatbuttonScroll(event);"/>
       <xul:scrollbox class="arrowscrollbox-scrollbox"
                      anonid="scrollbox"
                      flex="1"
                      xbl:inherits="orient,align,pack,dir">
         <children/>
       </xul:scrollbox>
       <xul:autorepeatbutton class="autorepeatbutton-down"
                             anonid="scrollbutton-down"
                             collapsed="true"
                             xbl:inherits="orient"
                             oncommand="_autorepeatbuttonScroll(event);"/>
     </content>
     <implementation>
       <destructor><![CDATA[
         this._stopSmoothScroll();
       ]]></destructor>
       <field name="_scrollbox">
         document.getAnonymousElementByAttribute(this, "anonid", "scrollbox");
       </field>
       <field name="_scrollButtonUp">
         document.getAnonymousElementByAttribute(this, "anonid", "scrollbutton-up");
       </field>
       <field name="_scrollButtonDown">
         document.getAnonymousElementByAttribute(this, "anonid", "scrollbutton-down");
       </field>
       <field name="__prefBranch">null</field>
       <property name="_prefBranch" readonly="true">
         <getter><![CDATA[
           if (this.__prefBranch === null) {
             this.__prefBranch = Components.classes['@mozilla.org/preferences-service;1']
                                           .getService(Components.interfaces.nsIPrefBranch);
           }
           return this.__prefBranch;
         ]]></getter>
       </property>
       <field name="_scrollIncrement">null</field>
       <property name="scrollIncrement" readonly="true">
         <getter><![CDATA[
           if (this._scrollIncrement === null) {
             try {
               this._scrollIncrement = this._prefBranch
                                           .getIntPref("toolkit.scrollbox.scrollIncrement");
             }
             catch (ex) {
               this._scrollIncrement = 20;
             }
           }
           return this._scrollIncrement;
         ]]></getter>
       </property>
       <field name="_smoothScroll">null</field>
       <property name="smoothScroll">
         <getter><![CDATA[
           if (this._smoothScroll === null) {
             if (this.hasAttribute("smoothscroll")) {
               this._smoothScroll = (this.getAttribute("smoothscroll") == "true");
             } else {
               try {
                 this._smoothScroll = this._prefBranch
                                          .getBoolPref("toolkit.scrollbox.smoothScroll");
               }
               catch (ex) {
                 this._smoothScroll = true;
               }
             }
           }
           return this._smoothScroll;
         ]]></getter>
         <setter><![CDATA[
           this._smoothScroll = val;
           return val;
         ]]></setter>
       </property>
       <field name="_scrollBoxObject">null</field>
       <property name="scrollBoxObject" readonly="true">
         <getter><![CDATA[
           if (!this._scrollBoxObject) {
             this._scrollBoxObject =
               this._scrollbox.boxObject
                              .QueryInterface(Components.interfaces.nsIScrollBoxObject);
           }
           return this._scrollBoxObject;
         ]]></getter>
       </property>
       <property name="scrollClientRect" readonly="true">
         <getter><![CDATA[
           return this._scrollbox.getBoundingClientRect();
         ]]></getter>
       </property>
       <property name="scrollClientSize" readonly="true">
         <getter><![CDATA[
           return this.orient == "vertical" ?
                  this._scrollbox.clientHeight :
                  this._scrollbox.clientWidth;
         ]]></getter>
       </property>
       <property name="scrollSize" readonly="true">
         <getter><![CDATA[
           return this.orient == "vertical" ?
                  this._scrollbox.scrollHeight :
                  this._scrollbox.scrollWidth;
         ]]></getter>
       </property>
       <property name="scrollPaddingRect" readonly="true">
         <getter><![CDATA[
           // This assumes that this._scrollbox doesn't have any border.
           var outerRect = this.scrollClientRect;
           var innerRect = {};
           innerRect.left = outerRect.left - this._scrollbox.scrollLeft;
           innerRect.top = outerRect.top - this._scrollbox.scrollTop;
           innerRect.right = innerRect.left + this._scrollbox.scrollWidth;
           innerRect.bottom = innerRect.top + this._scrollbox.scrollHeight;
           return innerRect;
         ]]></getter>
       </property>
       <property name="scrollboxPaddingStart" readonly="true">
         <getter><![CDATA[
           var ltr = (window.getComputedStyle(this, null).direction == "ltr");
           var paddingStartName = ltr ? "padding-left" : "padding-right";
           var scrollboxStyle = window.getComputedStyle(this._scrollbox, null);
           return parseFloat(scrollboxStyle.getPropertyValue(paddingStartName));
         ]]></getter>
       </property>
       <property name="scrollPosition">
         <getter><![CDATA[
           return this.orient == "vertical" ?
                  this._scrollbox.scrollTop :
                  this._scrollbox.scrollLeft;
         ]]></getter>
         <setter><![CDATA[
           if (this.orient == "vertical")
             this._scrollbox.scrollTop = val;
           else
             this._scrollbox.scrollLeft = val;
           return val;
         ]]></setter>
       </property>
       <property name="_startEndProps" readonly="true">
         <getter><![CDATA[
           return this.orient == "vertical" ?
                  ["top", "bottom"] : ["left", "right"];
         ]]></getter>
       </property>
       <field name="_isRTLScrollbox"><![CDATA[
         this.orient != "vertical" &&
         document.defaultView.getComputedStyle(this._scrollbox, "").direction == "rtl";
       ]]></field>
       <field name="_scrollTarget">null</field>
       <method name="_canScrollToElement">
         <parameter name="element"/>
         <body><![CDATA[
           return window.getComputedStyle(element).display != "none";
         ]]></body>
       </method>
       <method name="ensureElementIsVisible">
         <parameter name="element"/>
         <parameter name="aSmoothScroll"/>
         <body><![CDATA[
           if (!this._canScrollToElement(element))
             return;
           var vertical = this.orient == "vertical";
           var rect = this.scrollClientRect;
           var containerStart = vertical ? rect.top : rect.left;
           var containerEnd = vertical ? rect.bottom : rect.right;
           rect = element.getBoundingClientRect();
           var elementStart = vertical ? rect.top : rect.left;
           var elementEnd = vertical ? rect.bottom : rect.right;
           var scrollPaddingRect = this.scrollPaddingRect;
           let style = window.getComputedStyle(this._scrollbox, null);
           var scrollContentRect = {
             left: scrollPaddingRect.left + parseFloat(style.paddingLeft),
             top: scrollPaddingRect.top + parseFloat(style.paddingTop),
             right: scrollPaddingRect.right - parseFloat(style.paddingRight),
             bottom: scrollPaddingRect.bottom - parseFloat(style.paddingBottom)
           };
           // Provide an entry point for derived bindings to adjust these values.
           if (this._adjustElementStartAndEnd) {
             [elementStart, elementEnd] =
               this._adjustElementStartAndEnd(element, elementStart, elementEnd);
           }
           if (elementStart <= (vertical ? scrollContentRect.top : scrollContentRect.left)) {
             elementStart = vertical ? scrollPaddingRect.top : scrollPaddingRect.left;
           }
           if (elementEnd >= (vertical ? scrollContentRect.bottom : scrollContentRect.right)) {
             elementEnd = vertical ? scrollPaddingRect.bottom : scrollPaddingRect.right;
           }
           var amountToScroll;
           if (elementStart < containerStart) {
             amountToScroll = elementStart - containerStart;
           } else if (containerEnd < elementEnd) {
             amountToScroll = elementEnd - containerEnd;
           } else if (this._isScrolling) {
             // decelerate if a currently-visible element is selected during the scroll
             const STOP_DISTANCE = 15;
             if (this._isScrolling == -1 && elementStart - STOP_DISTANCE < containerStart)
               amountToScroll = elementStart - containerStart;
             else if (this._isScrolling == 1 && containerEnd - STOP_DISTANCE < elementEnd)
               amountToScroll = elementEnd - containerEnd;
             else
               amountToScroll = this._isScrolling * STOP_DISTANCE;
           } else {
             return;
           }
           this._stopSmoothScroll();
           if (aSmoothScroll != false && this.smoothScroll) {
             this._smoothScrollByPixels(amountToScroll, element);
           } else {
             this.scrollByPixels(amountToScroll);
           }
         ]]></body>
       </method>
       <method name="_smoothScrollByPixels">
         <parameter name="amountToScroll"/>
         <parameter name="element"/><!-- optional -->
         <body><![CDATA[
           this._stopSmoothScroll();
           if (amountToScroll == 0)
             return;
           this._scrollTarget = element;
           // Positive amountToScroll makes us scroll right (elements fly left), negative scrolls left.
           this._isScrolling = amountToScroll < 0 ? -1 : 1;
           this._scrollAnim.start(amountToScroll);
         ]]></body>
       </method>
       <field name="_scrollAnim"><![CDATA[({
         scrollbox: this,
         requestHandle: 0, /* 0 indicates there is no pending request */
         start: function scrollAnim_start(distance) {
           this.distance = distance;
           this.startPos = this.scrollbox.scrollPosition;
           this.duration = Math.min(1000, Math.round(50 * Math.sqrt(Math.abs(distance))));
           this.startTime = window.mozAnimationStartTime;
           if (!this.requestHandle)
             this.requestHandle = window.mozRequestAnimationFrame(this);
         },
         stop: function scrollAnim_stop() {
           window.mozCancelAnimationFrame(this.requestHandle);
           this.requestHandle = 0;
         },
         sample: function scrollAnim_handleEvent(timeStamp) {
           const timePassed = timeStamp - this.startTime;
           const pos = timePassed >= this.duration ? 1 :
 - Math.pow(1 - timePassed / this.duration, 4);
           this.scrollbox.scrollPosition = this.startPos + (this.distance * pos);
           if (pos == 1)
             this.scrollbox._stopSmoothScroll();
           else
             this.requestHandle = window.mozRequestAnimationFrame(this);
         }
       })]]></field>
       <method name="scrollByIndex">
         <parameter name="index"/>
         <parameter name="aSmoothScroll"/>
         <body><![CDATA[
           if (index == 0)
             return;
           // Each scrollByIndex call is expected to scroll the given number of
           // items. If a previous call is still in progress because of smooth
           // scrolling, we need to complete it before starting a new one.
           if (this._scrollTarget) {
             let elements = this._getScrollableElements();
             if (this._scrollTarget != elements[0] &&
                 this._scrollTarget != elements[elements.length - 1])
               this.ensureElementIsVisible(this._scrollTarget, false);
           }
           var rect = this.scrollClientRect;
           var [start, end] = this._startEndProps;
           var x = index > 0 ? rect[end] + 1 : rect[start] - 1;
           var nextElement = this._elementFromPoint(x, index);
           if (!nextElement)
             return;
           var targetElement;
           if (this._isRTLScrollbox)
             index *= -1;
           while (index < 0 && nextElement) {
             if (this._canScrollToElement(nextElement))
               targetElement = nextElement;
             nextElement = nextElement.previousSibling;
             index++;
           }
           while (index > 0 && nextElement) {
             if (this._canScrollToElement(nextElement))
               targetElement = nextElement;
             nextElement = nextElement.nextSibling;
             index--;
           }
           if (!targetElement)
             return;
           this.ensureElementIsVisible(targetElement, aSmoothScroll);
         ]]></body>
       </method>
       <method name="_getScrollableElements">
         <body><![CDATA[
           var nodes = this.childNodes;
           if (nodes.length == 1 &&
               nodes[0].localName == "children" &&
               nodes[0].namespaceURI == "http://www.mozilla.org/xbl") {
             nodes = document.getBindingParent(this).childNodes;
           }
           return Array.filter(nodes, this._canScrollToElement, this);
         ]]></body>
       </method>
       <method name="_elementFromPoint">
         <parameter name="aX"/>
         <parameter name="aPhysicalScrollDir"/>
         <body><![CDATA[
           var elements = this._getScrollableElements();
           if (!elements.length)
             return null;
           if (this._isRTLScrollbox)
             elements.reverse();
           var [start, end] = this._startEndProps;
           var low = 0;
           var high = elements.length - 1;
           if (aX < elements[low].getBoundingClientRect()[start] ||
               aX > elements[high].getBoundingClientRect()[end])
             return null;
           var mid, rect;
           while (low <= high) {
             mid = Math.floor((low + high) / 2);
             rect = elements[mid].getBoundingClientRect();
             if (rect[start] > aX)
               high = mid - 1;
             else if (rect[end] < aX)
               low = mid + 1;
             else
               return elements[mid];
           }
           // There's no element at the requested coordinate, but the algorithm
           // from above yields an element next to it, in a random direction.
           // The desired scrolling direction leads to the correct element.
           if (!aPhysicalScrollDir)
             return null;
           if (aPhysicalScrollDir < 0 && rect[start] > aX)
             mid = Math.max(mid - 1, 0);
           else if (aPhysicalScrollDir > 0 && rect[end] < aX)
             mid = Math.min(mid + 1, elements.length - 1);
           return elements[mid];
         ]]></body>
       </method>
       <method name="_autorepeatbuttonScroll">
         <parameter name="event"/>
         <body><![CDATA[
           var dir = event.originalTarget == this._scrollButtonUp ? -1 : 1;
           if (this._isRTLScrollbox)
             dir *= -1;
           this.scrollByPixels(this.scrollIncrement * dir);
           event.stopPropagation();
         ]]></body>
       </method>
       <method name="scrollByPixels">
         <parameter name="px"/>
         <body><![CDATA[
           this.scrollPosition += px;
         ]]></body>
       </method>
       <!-- 0: idle
 : scrolling right
           -1: scrolling left -->
       <field name="_isScrolling">0</field>
       <field name="_prevMouseScrolls">[null, null]</field>
       <method name="_stopSmoothScroll">
         <body><![CDATA[
           if (this._isScrolling) {
             this._scrollAnim.stop();
             this._isScrolling = 0;
             this._scrollTarget = null;
           }
         ]]></body>
       </method>
       <method name="_updateScrollButtonsDisabledState">
         <body><![CDATA[
           var disableUpButton = false;
           var disableDownButton = false;
           if (this.scrollPosition == 0) {
             // In the RTL case, this means the _last_ element in the
             // scrollbox is visible
             if (this._isRTLScrollbox)
               disableDownButton = true;
             else
               disableUpButton = true;
           }
           else if (this.scrollClientSize + this.scrollPosition == this.scrollSize) {
             // In the RTL case, this means the _first_ element in the
             // scrollbox is visible
             if (this._isRTLScrollbox)
               disableUpButton = true;
             else
               disableDownButton = true;
           }
           this._scrollButtonUp.disabled = disableUpButton;
           this._scrollButtonDown.disabled = disableDownButton;
         ]]></body>
       </method>
     </implementation>
     <handlers>
       <handler event="DOMMouseScroll"><![CDATA[
         if (this.orient == "vertical") {
           // prevent horizontal scrolling from scrolling a vertical scrollbox
           if (event.axis == event.HORIZONTAL_AXIS)
             return;
           this.scrollByIndex(event.detail);
         }
         // We allow vertical scrolling to scroll a horizontal scrollbox
         // because many users have a vertical scroll wheel but no
         // horizontal support.
         // Because of this, we need to avoid scrolling chaos on trackpads
         // and mouse wheels that support simultaneous scrolling in both axes.
         // We do this by scrolling only when the last two scroll events were
         // on the same axis as the current scroll event.
         else {
           let isVertical = event.axis == event.VERTICAL_AXIS;
           if (this._prevMouseScrolls.every(function(prev) prev == isVertical))
             this.scrollByIndex(isVertical && this._isRTLScrollbox ? -event.detail :
                                                                     event.detail);
           if (this._prevMouseScrolls.length > 1)
             this._prevMouseScrolls.shift();
           this._prevMouseScrolls.push(isVertical);
         }
         event.stopPropagation();
         event.preventDefault();
       ]]></handler>
       <handler event="MozMousePixelScroll"><![CDATA[
         event.stopPropagation();
         event.preventDefault();
       ]]></handler>
       <handler event="underflow" phase="capturing"><![CDATA[
         // filter underflow events which were dispatched on nested scrollboxes
         if (event.target != this)
           return;
         // Ignore events that doesn't match our orientation.
         // Scrollport event orientation:
         //   0: vertical
         //   1: horizontal
         //   2: both
         if (this.orient == "vertical") {
           if (event.detail == 1)
             return;
         }
         else {    // horizontal scrollbox
           if (event.detail == 0)
             return;
         }
         this._scrollButtonUp.collapsed = true;
         this._scrollButtonDown.collapsed = true;
         try {
           // See bug 341047 and comments in overflow handler as to why
           // try..catch is needed here
           let childNodes = this._getScrollableElements();
           if (childNodes && childNodes.length)
             this.ensureElementIsVisible(childNodes[0], false);
         }
         catch(e) {
           this._scrollButtonUp.collapsed = false;
           this._scrollButtonDown.collapsed = false;
         }
       ]]></handler>
       <handler event="overflow" phase="capturing"><![CDATA[
         // filter underflow events which were dispatched on nested scrollboxes
         if (event.target != this)
           return;
         // Ignore events that doesn't match our orientation.
         // Scrollport event orientation:
         //   0: vertical
         //   1: horizontal
         //   2: both
         if (this.orient == "vertical") {
           if (event.detail == 1)
             return;
         }
         else {    // horizontal scrollbox
           if (event.detail == 0)
             return;
         }
         this._scrollButtonUp.collapsed = false;
         this._scrollButtonDown.collapsed = false;
         try {
           // See bug 341047, the overflow event is dispatched when the
           // scrollbox already is mostly destroyed. This causes some code in
           // _updateScrollButtonsDisabledState() to throw an error. It also
           // means that the scrollbarbuttons were uncollapsed when that should
           // not be happening, because the whole overflow event should not be
           // happening in that case.
           this._updateScrollButtonsDisabledState();
         }
         catch(e) {
           this._scrollButtonUp.collapsed = true;
           this._scrollButtonDown.collapsed = true;
         }
       ]]></handler>
       <handler event="scroll" action="this._updateScrollButtonsDisabledState()"/>
     </handlers>
   </binding>
   <binding id="autorepeatbutton" extends="chrome://global/content/bindings/scrollbox.xml#scrollbox-base">
     <content repeat="hover">
       <xul:image class="autorepeatbutton-icon"/>
     </content>
   </binding>
   <binding id="arrowscrollbox-clicktoscroll" extends="chrome://global/content/bindings/scrollbox.xml#arrowscrollbox">
     <content>
       <xul:toolbarbutton class="scrollbutton-up" collapsed="true"
                          xbl:inherits="orient"
                          anonid="scrollbutton-up"
                          onclick="_distanceScroll(event);"
                          onmousedown="if (event.button == 0) _startScroll(-1);"
                          onmouseup="if (event.button == 0) _stopScroll();"
                          onmouseover="_continueScroll(-1);"
                          onmouseout="_pauseScroll();"/>
       <xul:scrollbox class="arrowscrollbox-scrollbox"
                      anonid="scrollbox"
                      flex="1"
                      xbl:inherits="orient,align,pack,dir">
         <children/>
       </xul:scrollbox>
       <xul:toolbarbutton class="scrollbutton-down" collapsed="true"
                          xbl:inherits="orient"
                          anonid="scrollbutton-down"
                          onclick="_distanceScroll(event);"
                          onmousedown="if (event.button == 0) _startScroll(1);"
                          onmouseup="if (event.button == 0) _stopScroll();"
                          onmouseover="_continueScroll(1);"
                          onmouseout="_pauseScroll();"/>
     </content>
     <implementation implements="nsITimerCallback, nsIDOMEventListener">
       <constructor><![CDATA[
         try {
           this._scrollDelay = this._prefBranch
                                   .getIntPref("toolkit.scrollbox.clickToScroll.scrollDelay");
         }
         catch (ex) {
         }
       ]]></constructor>
       <destructor><![CDATA[
         // Release timer to avoid reference cycles.
         if (this._scrollTimer) {
           this._scrollTimer.cancel();
           this._scrollTimer = null;
         }
       ]]></destructor>
       <field name="_scrollIndex">0</field>
       <field name="_scrollDelay">150</field>
       <method name="notify">
         <parameter name="aTimer"/>
         <body>
         <![CDATA[
           if (!document)
             aTimer.cancel();
           this.scrollByIndex(this._scrollIndex);
         ]]>
         </body>
       </method>
       <field name="_arrowScrollAnim"><![CDATA[({
         scrollbox: this,
         requestHandle: 0, /* 0 indicates there is no pending request */
         start: function arrowSmoothScroll_start() {
           this.lastFrameTime = window.mozAnimationStartTime;
           if (!this.requestHandle)
             this.requestHandle = window.mozRequestAnimationFrame(this);
         },
         stop: function arrowSmoothScroll_stop() {
           window.mozCancelAnimationFrame(this.requestHandle);
           this.requestHandle = 0;
         },
         sample: function arrowSmoothScroll_handleEvent(timeStamp) {
           const scrollIndex = this.scrollbox._scrollIndex;
           const timePassed = timeStamp - this.lastFrameTime;
           this.lastFrameTime = timeStamp;
           const scrollDelta = 0.5 * timePassed * scrollIndex;
           this.scrollbox.scrollPosition += scrollDelta;
           this.requestHandle = window.mozRequestAnimationFrame(this);
         }
       })]]></field>
       <method name="_startScroll">
         <parameter name="index"/>
         <body><![CDATA[
           if (this._isRTLScrollbox)
             index *= -1;
           this._scrollIndex = index;
           this._mousedown = true;
           if (this.smoothScroll) {
             this._arrowScrollAnim.start();
             return;
           }
           if (!this._scrollTimer)
             this._scrollTimer =
               Components.classes["@mozilla.org/timer;1"]
                         .createInstance(Components.interfaces.nsITimer);
           else
             this._scrollTimer.cancel();
           this._scrollTimer.initWithCallback(this, this._scrollDelay,
                                              this._scrollTimer.TYPE_REPEATING_SLACK);
           this.notify(this._scrollTimer);
         ]]>
         </body>
       </method>
       <method name="_stopScroll">
         <body><![CDATA[
           if (this._scrollTimer)
             this._scrollTimer.cancel();
           this._mousedown = false;
           if (!this._scrollIndex || !this.smoothScroll)
             return;
           this.scrollByIndex(this._scrollIndex);
           this._scrollIndex = 0;
           this._arrowScrollAnim.stop();
         ]]></body>
       </method>
       <method name="_pauseScroll">
         <body><![CDATA[
           if (this._mousedown) {
             this._stopScroll();
             this._mousedown = true;
             document.addEventListener("mouseup", this, false);
             document.addEventListener("blur", this, true);
           }
         ]]></body>
       </method>
       <method name="_continueScroll">
         <parameter name="index"/>
         <body><![CDATA[
           if (this._mousedown)
             this._startScroll(index);
         ]]></body>
       </method>
       <method name="handleEvent">
         <parameter name="aEvent"/>
         <body><![CDATA[
           if (aEvent.type == "mouseup" ||
               aEvent.type == "blur" && aEvent.target == document) {
             this._mousedown = false;
             document.removeEventListener("mouseup", this, false);
             document.removeEventListener("blur", this, true);
           }
         ]]></body>
       </method>
       <method name="_distanceScroll">
         <parameter name="aEvent"/>
         <body><![CDATA[
           if (aEvent.detail < 2 || aEvent.detail > 3)
             return;
           var scrollBack = (aEvent.originalTarget == this._scrollButtonUp);
           var scrollLeftOrUp = this._isRTLScrollbox ? !scrollBack : scrollBack;
           var targetElement;
           if (aEvent.detail == 2) {
             // scroll by the size of the scrollbox
             let [start, end] = this._startEndProps;
             let x;
             if (scrollLeftOrUp)
               x = this.scrollClientRect[start] - this.scrollClientSize;
             else
               x = this.scrollClientRect[end] + this.scrollClientSize;
             targetElement = this._elementFromPoint(x, scrollLeftOrUp ? -1 : 1);
             // the next partly-hidden element will become fully visible,
             // so don't scroll too far
             if (targetElement)
               targetElement = scrollBack ?
                               targetElement.nextSibling :
                               targetElement.previousSibling;
           }
           if (!targetElement) {
             // scroll to the first resp. last element
             let elements = this._getScrollableElements();
             targetElement = scrollBack ?
                             elements[0] :
                             elements[elements.length - 1];
           }
           this.ensureElementIsVisible(targetElement);
         ]]></body>
       </method>
     </implementation>
   </binding>
 </bindings>

The Tor Browser / annotate

toolkit/content/widgets/scrollbox.xml@6474c204b198 (annotated)

toolkit/content/widgets/scrollbox.xml