diff -r 000000000000 -r 6474c204b198 browser/devtools/framework/test/browser_toolbox_zoom.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/devtools/framework/test/browser_toolbox_zoom.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,67 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+let modifiers = {
+  accelKey: true
+};
+
+let toolbox;
+
+function test() {
+  waitForExplicitFinish();
+
+  addTab("about:blank", function() {
+    openToolbox();
+  });
+}
+
+function openToolbox() {
+  let target = TargetFactory.forTab(gBrowser.selectedTab);
+
+  gDevTools.showToolbox(target).then((aToolbox) => {
+    toolbox = aToolbox;
+    toolbox.selectTool("styleeditor").then(testZoom);
+  });
+}
+
+function testZoom() {
+  info("testing zoom keys");
+
+  testZoomLevel("in", 2, 1.2);
+  testZoomLevel("out", 3, 0.9);
+  testZoomLevel("reset", 1, 1);
+
+  tidyUp();
+}
+
+function testZoomLevel(type, times, expected) {
+  sendZoomKey("toolbox-zoom-"+ type + "-key", times);
+
+  let zoom = getCurrentZoom(toolbox);
+  is(zoom.toFixed(2), expected, "zoom level correct after zoom " + type);
+
+  is(toolbox.zoomValue.toFixed(2), expected,
+     "saved zoom level is correct after zoom " + type);
+}
+
+function sendZoomKey(id, times) {
+  let key = toolbox.doc.getElementById(id).getAttribute("key");
+  for (let i = 0; i < times; i++) {
+    EventUtils.synthesizeKey(key, modifiers, toolbox.doc.defaultView);
+  }
+}
+
+function getCurrentZoom() {
+  var contViewer = toolbox.frame.docShell.contentViewer;
+  var docViewer = contViewer.QueryInterface(Ci.nsIMarkupDocumentViewer);
+  return docViewer.fullZoom;
+}
+
+function tidyUp() {
+  toolbox.destroy().then(function() {
+    gBrowser.removeCurrentTab();
+
+    toolbox = modifiers = null;
+    finish();
+  });
+}