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diff --git a/android/source/src/java/org/mozilla/gecko/gfx/TouchEventHandler.java b/android/source/src/java/org/mozilla/gecko/gfx/TouchEventHandler.java
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+/* -*- Mode: Java; c-basic-offset: 4; tab-width: 20; indent-tabs-mode: nil; -*-
+ * 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.gfx;
+
+import android.content.Context;
+import android.os.SystemClock;
+import android.util.Log;
+import android.view.GestureDetector;
+import android.view.MotionEvent;
+import android.view.View;
+
+import java.util.LinkedList;
+import java.util.Queue;
+
+/**
+ * This class handles incoming touch events from the user and sends them to
+ * listeners in Gecko and/or performs the "default action" (asynchronous pan/zoom
+ * behaviour. EVERYTHING IN THIS CLASS MUST RUN ON THE UI THREAD.
+ *
+ * In the following code/comments, a "block" of events refers to a contiguous
+ * sequence of events that starts with a DOWN or POINTER_DOWN and goes up to
+ * but not including the next DOWN or POINTER_DOWN event.
+ *
+ * "Dispatching" an event refers to performing the default actions for the event,
+ * which at our level of abstraction just means sending it off to the gesture
+ * detectors and the pan/zoom controller.
+ *
+ * If an event is "default-prevented" that means one or more listeners in Gecko
+ * has called preventDefault() on the event, which means that the default action
+ * for that event should not occur. Usually we care about a "block" of events being
+ * default-prevented, which means that the DOWN/POINTER_DOWN event that started
+ * the block, or the first MOVE event following that, were prevent-defaulted.
+ *
+ * A "default-prevented notification" is when we here in Java-land receive a notification
+ * from gecko as to whether or not a block of events was default-prevented. This happens
+ * at some point after the first or second event in the block is processed in Gecko.
+ * This code assumes we get EXACTLY ONE default-prevented notification for each block
+ * of events.
+ *
+ * Note that even if all events are default-prevented, we still send specific types
+ * of notifications to the pan/zoom controller. The notifications are needed
+ * to respond to user actions a timely manner regardless of default-prevention,
+ * and fix issues like bug 749384.
+ */
+public final class TouchEventHandler {
+    private static final String LOGTAG = "GeckoTouchEventHandler";
+
+    // The time limit for listeners to respond with preventDefault on touchevents
+    // before we begin panning the page
+    private final int EVENT_LISTENER_TIMEOUT = 200;
+
+    private final View mView;
+    private final GestureDetector mGestureDetector;
+    private final SimpleScaleGestureDetector mScaleGestureDetector;
+    private final JavaPanZoomController mPanZoomController;
+
+    // the queue of events that we are holding on to while waiting for a preventDefault
+    // notification
+    private final Queue<MotionEvent> mEventQueue;
+    private final ListenerTimeoutProcessor mListenerTimeoutProcessor;
+
+    // whether or not we should wait for touch listeners to respond (this state is
+    // per-tab and is updated when we switch tabs).
+    private boolean mWaitForTouchListeners;
+
+    // true if we should hold incoming events in our queue. this is re-set for every
+    // block of events, this is cleared once we find out if the block has been
+    // default-prevented or not (or we time out waiting for that).
+    private boolean mHoldInQueue;
+
+    // true if we should dispatch incoming events to the gesture detector and the pan/zoom
+    // controller. if this is false, then the current block of events has been
+    // default-prevented, and we should not dispatch these events (although we'll still send
+    // them to gecko listeners).
+    private boolean mDispatchEvents;
+
+    // this next variable requires some explanation. strap yourself in.
+    //
+    // for each block of events, we do two things: (1) send the events to gecko and expect
+    // exactly one default-prevented notification in return, and (2) kick off a delayed
+    // ListenerTimeoutProcessor that triggers in case we don't hear from the listener in
+    // a timely fashion.
+    // since events are constantly coming in, we need to be able to handle more than one
+    // block of events in the queue.
+    //
+    // this means that there are ordering restrictions on these that we can take advantage of,
+    // and need to abide by. blocks of events in the queue will always be in the order that
+    // the user generated them. default-prevented notifications we get from gecko will be in
+    // the same order as the blocks of events in the queue. the ListenerTimeoutProcessors that
+    // have been posted will also fire in the same order as the blocks of events in the queue.
+    // HOWEVER, we may get multiple default-prevented notifications interleaved with multiple
+    // ListenerTimeoutProcessor firings, and that interleaving is not predictable.
+    //
+    // therefore, we need to make sure that for each block of events, we process the queued
+    // events exactly once, either when we get the default-prevented notification, or when the
+    // timeout expires (whichever happens first). there is no way to associate the
+    // default-prevented notification with a particular block of events other than via ordering,
+    //
+    // so what we do to accomplish this is to track a "processing balance", which is the number
+    // of default-prevented notifications that we have received, minus the number of ListenerTimeoutProcessors
+    // that have fired. (think "balance" as in teeter-totter balance). this value is:
+    // - zero when we are in a state where the next default-prevented notification we expect
+    //   to receive and the next ListenerTimeoutProcessor we expect to fire both correspond to
+    //   the next block of events in the queue.
+    // - positive when we are in a state where we have received more default-prevented notifications
+    //   than ListenerTimeoutProcessors. This means that the next default-prevented notification
+    //   does correspond to the block at the head of the queue, but the next n ListenerTimeoutProcessors
+    //   need to be ignored as they are for blocks we have already processed. (n is the absolute value
+    //   of the balance.)
+    // - negative when we are in a state where we have received more ListenerTimeoutProcessors than
+    //   default-prevented notifications. This means that the next ListenerTimeoutProcessor that
+    //   we receive does correspond to the block at the head of the queue, but the next n
+    //   default-prevented notifications need to be ignored as they are for blocks we have already
+    //   processed. (n is the absolute value of the balance.)
+    private int mProcessingBalance;
+
+    TouchEventHandler(Context context, View view, JavaPanZoomController panZoomController) {
+        mView = view;
+
+        mEventQueue = new LinkedList<MotionEvent>();
+        mPanZoomController = panZoomController;
+        mGestureDetector = new GestureDetector(context, mPanZoomController);
+        mScaleGestureDetector = new SimpleScaleGestureDetector(mPanZoomController);
+        mListenerTimeoutProcessor = new ListenerTimeoutProcessor();
+        mDispatchEvents = true;
+
+        mGestureDetector.setOnDoubleTapListener(mPanZoomController);
+    }
+
+    void destroy() {
+    }
+
+    /* This function MUST be called on the UI thread */
+    public boolean handleEvent(MotionEvent event) {
+        if (isDownEvent(event)) {
+            // this is the start of a new block of events! whee!
+            mHoldInQueue = mWaitForTouchListeners;
+
+            // Set mDispatchEvents to true so that we are guaranteed to either queue these
+            // events or dispatch them. The only time we should not do either is once we've
+            // heard back from content to preventDefault this block.
+            mDispatchEvents = true;
+            if (mHoldInQueue) {
+                // if the new block we are starting is the current block (i.e. there are no
+                // other blocks waiting in the queue, then we should let the pan/zoom controller
+                // know we are waiting for the touch listeners to run
+                if (mEventQueue.isEmpty()) {
+                    mPanZoomController.startingNewEventBlock(event, true);
+                }
+            } else {
+                // we're not going to be holding this block of events in the queue, but we need
+                // a marker of some sort so that the processEventBlock loop deals with the blocks
+                // in the right order as notifications come in. we use a single null event in
+                // the queue as a placeholder for a block of events that has already been dispatched.
+                mEventQueue.add(null);
+                mPanZoomController.startingNewEventBlock(event, false);
+            }
+
+            // set the timeout so that we dispatch these events and update mProcessingBalance
+            // if we don't get a default-prevented notification
+            mView.postDelayed(mListenerTimeoutProcessor, EVENT_LISTENER_TIMEOUT);
+        }
+
+        // if we need to hold the events, add it to the queue. if we need to dispatch
+        // it directly, do that. it is possible that both mHoldInQueue and mDispatchEvents
+        // are false, in which case we are processing a block of events that we know
+        // has been default-prevented. in that case we don't keep the events as we don't
+        // need them (but we still pass them to the gecko listener).
+        if (mHoldInQueue) {
+            mEventQueue.add(MotionEvent.obtain(event));
+        } else if (mDispatchEvents) {
+            dispatchEvent(event);
+        } else if (touchFinished(event)) {
+            mPanZoomController.preventedTouchFinished();
+        }
+
+        return true;
+    }
+
+    /**
+     * This function is how gecko sends us a default-prevented notification. It is called
+     * once gecko knows definitively whether the block of events has had preventDefault
+     * called on it (either on the initial down event that starts the block, or on
+     * the first event following that down event).
+     *
+     * This function MUST be called on the UI thread.
+     */
+    public void handleEventListenerAction(boolean allowDefaultAction) {
+        if (mProcessingBalance > 0) {
+            // this event listener that triggered this took too long, and the corresponding
+            // ListenerTimeoutProcessor runnable already ran for the event in question. the
+            // block of events this is for has already been processed, so we don't need to
+            // do anything here.
+        } else {
+            processEventBlock(allowDefaultAction);
+        }
+        mProcessingBalance--;
+    }
+
+    /* This function MUST be called on the UI thread. */
+    public void setWaitForTouchListeners(boolean aValue) {
+        mWaitForTouchListeners = aValue;
+    }
+
+    private boolean isDownEvent(MotionEvent event) {
+        int action = (event.getAction() & MotionEvent.ACTION_MASK);
+        return (action == MotionEvent.ACTION_DOWN || action == MotionEvent.ACTION_POINTER_DOWN);
+    }
+
+    private boolean touchFinished(MotionEvent event) {
+        int action = (event.getAction() & MotionEvent.ACTION_MASK);
+        return (action == MotionEvent.ACTION_UP || action == MotionEvent.ACTION_CANCEL);
+    }
+
+    /**
+     * Dispatch the event to the gesture detectors and the pan/zoom controller.
+     */
+    private void dispatchEvent(MotionEvent event) {
+        if (mGestureDetector.onTouchEvent(event)) {
+            return;
+        }
+        mScaleGestureDetector.onTouchEvent(event);
+        if (mScaleGestureDetector.isInProgress()) {
+            return;
+        }
+        mPanZoomController.handleEvent(event);
+    }
+
+    /**
+     * Process the block of events at the head of the queue now that we know
+     * whether it has been default-prevented or not.
+     */
+    private void processEventBlock(boolean allowDefaultAction) {
+        if (!allowDefaultAction) {
+            // if the block has been default-prevented, cancel whatever stuff we had in
+            // progress in the gesture detector and pan zoom controller
+            long now = SystemClock.uptimeMillis();
+            dispatchEvent(MotionEvent.obtain(now, now, MotionEvent.ACTION_CANCEL, 0, 0, 0));
+        }
+
+        if (mEventQueue.isEmpty()) {
+            Log.e(LOGTAG, "Unexpected empty event queue in processEventBlock!", new Exception());
+            return;
+        }
+
+        // the odd loop condition is because the first event in the queue will
+        // always be a DOWN or POINTER_DOWN event, and we want to process all
+        // the events in the queue starting at that one, up to but not including
+        // the next DOWN or POINTER_DOWN event.
+
+        MotionEvent event = mEventQueue.poll();
+        while (true) {
+            // event being null here is valid and represents a block of events
+            // that has already been dispatched.
+
+            if (event != null) {
+                // for each event we process, only dispatch it if the block hasn't been
+                // default-prevented.
+                if (allowDefaultAction) {
+                    dispatchEvent(event);
+                } else if (touchFinished(event)) {
+                    mPanZoomController.preventedTouchFinished();
+                }
+            }
+            if (mEventQueue.isEmpty()) {
+                // we have processed the backlog of events, and are all caught up.
+                // now we can set clear the hold flag and set the dispatch flag so
+                // that the handleEvent() function can do the right thing for all
+                // remaining events in this block (which is still ongoing) without
+                // having to put them in the queue.
+                mHoldInQueue = false;
+                mDispatchEvents = allowDefaultAction;
+                break;
+            }
+            event = mEventQueue.peek();
+            if (event == null || isDownEvent(event)) {
+                // we have finished processing the block we were interested in.
+                // now we wait for the next call to processEventBlock
+                if (event != null) {
+                    mPanZoomController.startingNewEventBlock(event, true);
+                }
+                break;
+            }
+            // pop the event we peeked above, as it is still part of the block and
+            // we want to keep processing
+            mEventQueue.remove();
+        }
+    }
+
+    private class ListenerTimeoutProcessor implements Runnable {
+        /* This MUST be run on the UI thread */
+        public void run() {
+            if (mProcessingBalance < 0) {
+                // gecko already responded with default-prevented notification, and so
+                // the block of events this ListenerTimeoutProcessor corresponds to have
+                // already been removed from the queue.
+            } else {
+                processEventBlock(true);
+            }
+            mProcessingBalance++;
+        }
+    }
+}