diff -r 000000000000 -r 6474c204b198 browser/metro/modules/colorUtils.jsm
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/metro/modules/colorUtils.jsm	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,173 @@
+// -*- Mode: js2; tab-width: 2; indent-tabs-mode: nil; js2-basic-offset: 2; js2-skip-preprocessor-directives: t; -*-
+/* 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/. */
+'use strict';
+Components.utils.import("resource://gre/modules/Services.jsm");
+Components.utils.import("resource://gre/modules/Promise.jsm");
+
+const ColorAnalyzer = Components.classes["@mozilla.org/places/colorAnalyzer;1"]
+                .getService(Components.interfaces.mozIColorAnalyzer);
+
+this.EXPORTED_SYMBOLS = ["ColorUtils"];
+
+let ColorUtils = {
+  _initialized: false,
+  init: function() {
+    if (this._initialized)
+        return;
+    Services.obs.addObserver(this, "idle-daily", false);
+    Services.obs.addObserver(this, "quit-application", false);
+    this._initialized = true;
+  },
+  uninit: function() {
+    Services.obs.removeObserver(this, "idle-daily");
+    Services.obs.removeObserver(this, "quit-application");
+  },
+
+  // default to keeping icon colorInfo for max 1 day
+  iconColorCacheMaxAge: 86400000,
+
+  // in-memory store for favicon color data
+  _uriColorsMap: (function() {
+    let cache = new Map();
+    // remove stale entries
+    cache.purge = function(maxAgeMs = 0) {
+      let cuttoff = Date.now() - (maxAgeMs || ColorUtils.iconColorCacheMaxAge);
+      for (let [key, value] of this) {
+        if (value.timestamp && value.timestamp >= cuttoff) {
+          continue;
+        }
+        this.delete(key);
+      }
+    }
+    return cache;
+  })(),
+  get iconColorCache() {
+    return ColorUtils._uriColorsMap;
+  },
+
+  observe: function (aSubject, aTopic, aData) {
+    switch (aTopic) {
+      case "idle-daily":
+        this.iconColorCache.purge();
+        break;
+      case "quit-application":
+        this.uninit();
+        break;
+    }
+  },
+
+  /** Takes an icon and returns either an object with foreground and background color properties
+   *  or a promise for the same.
+   *  The foreground is the contrast color, the background is the primary/dominant one
+   */
+  getForegroundAndBackgroundIconColors: function getForegroundAndBackgroundIconColors(aIconURI) {
+    let colorKey = aIconURI.spec;
+    let colorInfo = this._uriColorsMap.get(colorKey);
+    if (colorInfo) {
+      return colorInfo;
+    }
+
+    let deferred = Promise.defer();
+    let wrappedIcon = aIconURI;
+    this._uriColorsMap.set(colorKey, deferred.promise);
+
+    ColorAnalyzer.findRepresentativeColor(wrappedIcon, (success, color) => {
+      if (!success) {
+        this._uriColorsMap.delete(colorKey);
+        deferred.reject();
+      } else {
+        colorInfo = {
+          foreground: this.bestTextColorForContrast(color),
+          background: this.convertDecimalToRgbColor(color),
+          timestamp: Date.now()
+        };
+        deferred.resolve(colorInfo);
+      }
+    });
+    return deferred.promise;
+  },
+
+  /** returns the best color for text readability on top of aColor
+   * return color is in rgb(r,g,b) format, suitable to csss
+   * The color bightness algorithm is currently: http://www.w3.org/TR/AERT#color-contrast
+   */
+  bestTextColorForContrast: function bestTextColorForContrast(aColor) {
+    let r = (aColor & 0xff0000) >> 16;
+    let g = (aColor & 0x00ff00) >> 8;
+    let b = (aColor & 0x0000ff);
+
+    let w3cContrastValue = ((r*299)+(g*587)+(b*114))/1000;
+    w3cContrastValue = Math.round(w3cContrastValue);
+    let textColor = "rgb(255,255,255)";
+
+    if (w3cContrastValue > 125) {
+      // bright/light, use black text
+      textColor = "rgb(0,0,0)";
+    }
+    return textColor;
+  },
+
+  toCSSRgbColor: function toCSSRgbColor(r, g, b, a) {
+    var values = [Math.round(r), Math.round(g), Math.round(b)];
+    if (undefined !== a && a < 1) {
+      values.push(a);
+      return 'rgba('+values.join(',')+')';
+    }
+    return 'rgb('+values.join(',')+')';
+  },
+
+  /**
+   * converts a decimal(base10) number into CSS rgb color value string
+   */
+  convertDecimalToRgbColor: function convertDecimalToRgbColor(aColor) {
+    let [r,g,b,a] = this.unpackDecimalColorWord(aColor);
+    return this.toCSSRgbColor(r,g,b,a);
+  },
+
+  /**
+   * unpack a decimal(base10) word for r,g,b,a values
+   */
+  unpackDecimalColorWord: function unpackDecimalColorWord(aColor) {
+    let a = (aColor & 0xff000000) >> 24;
+    let r = (aColor & 0x00ff0000) >> 16;
+    let g = (aColor & 0x0000ff00) >> 8;
+    let b = (aColor & 0x000000ff);
+    // NB: falsy alpha treated as undefined, fully opaque
+    return a ? [r,g,b,a/255] : [r,g,b];
+  },
+
+  /**
+   * create a decimal(base10) word for r,g,b values
+   */
+  createDecimalColorWord: function createDecimalColorWord(r, g, b, a) {
+    let rgb = 0;
+    rgb |= b;
+    rgb |= (g << 8);
+    rgb |= (r << 16);
+    // pack alpha value if one is given
+    if (undefined !== a && a < 1)
+      rgb |= (Math.round(a*255) << 24);
+    return rgb;
+  },
+
+  /**
+   * Add 2 rgb(a) colors to get a flat color
+   */
+  addRgbColors: function addRgbColors(color1, color2) {
+    let [r1, g1, b1] = this.unpackDecimalColorWord(color1);
+    let [r2, g2, b2, alpha] = this.unpackDecimalColorWord(color2);
+
+    let color = {};
+    // early return if 2nd color is opaque
+    if (!alpha || alpha >= 1)
+      return color2;
+
+    return this.createDecimalColorWord(
+      Math.min(255, alpha * r2 + (1 - alpha) * r1),
+      Math.min(255, alpha * g2 + (1 - alpha) * g1),
+      Math.min(255, alpha * b2 + (1 - alpha) * b1)
+    );
+  }
+};