diff -r 000000000000 -r 6474c204b198 mobile/android/base/favicons/decoders/IconDirectoryEntry.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mobile/android/base/favicons/decoders/IconDirectoryEntry.java	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,201 @@
+/* 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/. */
+
+package org.mozilla.gecko.favicons.decoders;
+
+/**
+ * Representation of an ICO file ICONDIRENTRY structure.
+ */
+public class IconDirectoryEntry implements Comparable<IconDirectoryEntry> {
+
+    public static int maxBPP;
+
+    int width;
+    int height;
+    int paletteSize;
+    int bitsPerPixel;
+    int payloadSize;
+    int payloadOffset;
+    boolean payloadIsPNG;
+
+    // Tracks the index in the Icon Directory of this entry. Useful only for pruning.
+    int index;
+    boolean isErroneous;
+
+    public IconDirectoryEntry(int width, int height, int paletteSize, int bitsPerPixel, int payloadSize, int payloadOffset, boolean payloadIsPNG) {
+        this.width = width;
+        this.height = height;
+        this.paletteSize = paletteSize;
+        this.bitsPerPixel = bitsPerPixel;
+        this.payloadSize = payloadSize;
+        this.payloadOffset = payloadOffset;
+        this.payloadIsPNG = payloadIsPNG;
+    }
+
+    /**
+     * Method to get a dummy Icon Directory Entry with the Erroneous bit set.
+     *
+     * @return An erroneous placeholder Icon Directory Entry.
+     */
+    public static IconDirectoryEntry getErroneousEntry() {
+        IconDirectoryEntry ret = new IconDirectoryEntry(-1, -1, -1, -1, -1, -1, false);
+        ret.isErroneous = true;
+
+        return ret;
+    }
+
+    /**
+     * Create an IconDirectoryEntry object from a byte[]. Interprets the buffer starting at the given
+     * offset as an IconDirectoryEntry and returns the result.
+     *
+     * @param buffer Byte array containing the icon directory entry to decode.
+     * @param regionOffset Offset into the byte array of the valid region of the buffer.
+     * @param regionLength Length of the valid region in the buffer.
+     * @param entryOffset Offset of the icon directory entry to decode within the buffer.
+     * @return An IconDirectoryEntry object representing the entry specified, or null if the entry
+     *         is obviously invalid.
+     */
+    public static IconDirectoryEntry createFromBuffer(byte[] buffer, int regionOffset, int regionLength, int entryOffset) {
+        // Verify that the reserved field is really zero.
+        if (buffer[entryOffset + 3] != 0) {
+            return getErroneousEntry();
+        }
+
+        // Verify that the entry points to a region that actually exists in the buffer, else bin it.
+        int fieldPtr = entryOffset + 8;
+        int entryLength = (buffer[fieldPtr] & 0xFF) |
+                          (buffer[fieldPtr + 1] & 0xFF) << 8 |
+                          (buffer[fieldPtr + 2] & 0xFF) << 16 |
+                          (buffer[fieldPtr + 3] & 0xFF) << 24;
+
+        // Advance to the offset field.
+        fieldPtr += 4;
+
+        int payloadOffset = (buffer[fieldPtr] & 0xFF) |
+                            (buffer[fieldPtr + 1] & 0xFF) << 8 |
+                            (buffer[fieldPtr + 2] & 0xFF) << 16 |
+                            (buffer[fieldPtr + 3] & 0xFF) << 24;
+
+        // Fail if the entry describes a region outside the buffer.
+        if (payloadOffset < 0 || entryLength < 0 || payloadOffset + entryLength > regionOffset + regionLength) {
+            return getErroneousEntry();
+        }
+
+        // Extract the image dimensions.
+        int imageWidth = buffer[entryOffset] & 0xFF;
+        int imageHeight = buffer[entryOffset+1] & 0xFF;
+
+        // Because Microsoft, a size value of zero represents an image size of 256.
+        if (imageWidth == 0) {
+            imageWidth = 256;
+        }
+
+        if (imageHeight == 0) {
+            imageHeight = 256;
+        }
+
+        // If the image uses a colour palette, this is the number of colours, otherwise this is zero.
+        int paletteSize = buffer[entryOffset + 2] & 0xFF;
+
+        // The plane count - usually 0 or 1. When > 1, taken as multiplier on bitsPerPixel.
+        int colorPlanes = buffer[entryOffset + 4] & 0xFF;
+
+        int bitsPerPixel = (buffer[entryOffset + 6] & 0xFF) |
+                           (buffer[entryOffset + 7] & 0xFF) << 8;
+
+        if (colorPlanes > 1) {
+            bitsPerPixel *= colorPlanes;
+        }
+
+        // Look for PNG magic numbers at the start of the payload.
+        boolean payloadIsPNG = FaviconDecoder.bufferStartsWith(buffer, FaviconDecoder.ImageMagicNumbers.PNG.value, regionOffset + payloadOffset);
+
+        return new IconDirectoryEntry(imageWidth, imageHeight, paletteSize, bitsPerPixel, entryLength, payloadOffset, payloadIsPNG);
+    }
+
+    /**
+     * Get the number of bytes from the start of the ICO file to the beginning of this entry.
+     */
+    public int getOffset() {
+        return ICODecoder.ICO_HEADER_LENGTH_BYTES + (index * ICODecoder.ICO_ICONDIRENTRY_LENGTH_BYTES);
+    }
+
+    @Override
+    public int compareTo(IconDirectoryEntry another) {
+        if (width > another.width) {
+            return 1;
+        }
+
+        if (width < another.width) {
+            return -1;
+        }
+
+        // Where both images exceed the max BPP, take the smaller of the two BPP values.
+        if (bitsPerPixel >= maxBPP && another.bitsPerPixel >= maxBPP) {
+            if (bitsPerPixel < another.bitsPerPixel) {
+                return 1;
+            }
+
+            if (bitsPerPixel > another.bitsPerPixel) {
+                return -1;
+            }
+        }
+
+        // Otherwise, take the larger of the BPP values.
+        if (bitsPerPixel > another.bitsPerPixel) {
+            return 1;
+        }
+
+        if (bitsPerPixel < another.bitsPerPixel) {
+            return -1;
+        }
+
+        // Prefer large palettes.
+        if (paletteSize > another.paletteSize) {
+            return 1;
+        }
+
+        if (paletteSize < another.paletteSize) {
+            return -1;
+        }
+
+        // Prefer smaller payloads.
+        if (payloadSize < another.payloadSize) {
+            return 1;
+        }
+
+        if (payloadSize > another.payloadSize) {
+            return -1;
+        }
+
+        // If all else fails, prefer PNGs over BMPs. They tend to be smaller.
+        if (payloadIsPNG && !another.payloadIsPNG) {
+            return 1;
+        }
+
+        if (!payloadIsPNG && another.payloadIsPNG) {
+            return -1;
+        }
+
+        return 0;
+    }
+
+    public static void setMaxBPP(int maxBPP) {
+        IconDirectoryEntry.maxBPP = maxBPP;
+    }
+
+    @Override
+    public String toString() {
+        return "IconDirectoryEntry{" +
+                "\nwidth=" + width +
+                ", \nheight=" + height +
+                ", \npaletteSize=" + paletteSize +
+                ", \nbitsPerPixel=" + bitsPerPixel +
+                ", \npayloadSize=" + payloadSize +
+                ", \npayloadOffset=" + payloadOffset +
+                ", \npayloadIsPNG=" + payloadIsPNG +
+                ", \nindex=" + index +
+                '}';
+    }
+}