diff --git a/dom/browser-element/BrowserElementParent.js b/dom/browser-element/BrowserElementParent.js
index 8ba375ad8cbc..701dcd87b186 100644
--- a/dom/browser-element/BrowserElementParent.js
+++ b/dom/browser-element/BrowserElementParent.js
@@ -539,7 +539,24 @@ BrowserElementParent.prototype = {
     return this._frameLoader.visible;
   },
 
+  getChildProcessOffset: function() {
+    let offset = { x: 0, y: 0 };
+    let tabParent = this._frameLoader.tabParent;
+    if (tabParent) {
+      let offsetX = {};
+      let offsetY = {};
+      tabParent.getChildProcessOffset(offsetX, offsetY);
+      offset.x = offsetX.value;
+      offset.y = offsetY.value;
+    }
+    return offset;
+  },
+
   sendMouseEvent: defineNoReturnMethod(function(type, x, y, button, clickCount, modifiers) {
+    let offset = this.getChildProcessOffset();
+    x += offset.x;
+    y += offset.y;
+
     this._sendAsyncMsg("send-mouse-event", {
       "type": type,
       "x": x,
@@ -567,6 +584,13 @@ BrowserElementParent.prototype = {
                                  count,
                                  modifiers);
     } else {
+      let offset = this.getChildProcessOffset();
+      for (var i = 0; i < touchesX.length; i++) {
+        touchesX[i] += offset.x;
+      }
+      for (var i = 0; i < touchesY.length; i++) {
+        touchesY[i] += offset.y;
+      }
       this._sendAsyncMsg("send-touch-event", {
         "type": type,
         "identifiers": identifiers,
diff --git a/dom/browser-element/mochitest/browserElement_SendEvent.js b/dom/browser-element/mochitest/browserElement_SendEvent.js
index 57f09e9be3cd..88e65d96fc13 100644
--- a/dom/browser-element/mochitest/browserElement_SendEvent.js
+++ b/dom/browser-element/mochitest/browserElement_SendEvent.js
@@ -12,9 +12,26 @@ function runTest() {
   var iframe = document.createElement("iframe");
   iframe.setAttribute('mozbrowser', 'true');
   document.body.appendChild(iframe);
+  var x = 10;
+  var y = 10;
+  // First we force a reflow so that getChildProcessOffset actually returns
+  // meaningful data.
+  iframe.getBoundingClientRect();
+  // We need to make sure the event coordinates are actually inside the iframe,
+  // relative to the chome window.
+  var tabParent = SpecialPowers.wrap(iframe)
+                  .QueryInterface(SpecialPowers.Ci.nsIFrameLoaderOwner)
+                  .frameLoader.tabParent;
+  if (tabParent) {
+    let offsetX = {};
+    let offsetY = {};
+    tabParent.getChildProcessOffset(offsetX, offsetY);
+    x -= offsetX.value;
+    y -= offsetY.value;
+  }
 
   iframe.addEventListener("mozbrowserloadend", function onloadend(e) {
-    iframe.sendMouseEvent("mousedown", 10, 10, 0, 1, 0);
+    iframe.sendMouseEvent("mousedown", x, y, 0, 1, 0);
   });
 
   iframe.addEventListener("mozbrowserlocationchange", function onlocchange(e) {
@@ -24,11 +41,11 @@ function runTest() {
     switch (a.hash) {
       case "#mousedown":
         ok(true, "Receive a mousedown event.");
-        iframe.sendMouseEvent("mousemove", 10, 10, 0, 0, 0);
+        iframe.sendMouseEvent("mousemove", x, y, 0, 0, 0);
         break;
       case "#mousemove":
         ok(true, "Receive a mousemove event.");
-        iframe.sendMouseEvent("mouseup", 10, 10, 0, 1, 0);
+        iframe.sendMouseEvent("mouseup", x, y, 0, 1, 0);
         break;
       case "#mouseup":
         ok(true, "Receive a mouseup event.");
@@ -36,7 +53,7 @@ function runTest() {
       case "#click":
         ok(true, "Receive a click event.");
         if (SpecialPowers.getIntPref("dom.w3c_touch_events.enabled") != 0) {
-          iframe.sendTouchEvent("touchstart", [1], [10], [10], [2], [2],
+          iframe.sendTouchEvent("touchstart", [1], [x], [y], [2], [2],
                                 [20], [0.5], 1, 0);
         } else {
           iframe.removeEventListener('mozbrowserlocationchange', onlocchange);
@@ -45,16 +62,16 @@ function runTest() {
         break;
       case "#touchstart":
         ok(true, "Receive a touchstart event.");
-        iframe.sendTouchEvent("touchmove", [1], [10], [10], [2], [2],
+        iframe.sendTouchEvent("touchmove", [1], [x], [y], [2], [2],
                               [20], [0.5], 1, 0);
       case "#touchmove":
         ok(true, "Receive a touchmove event.");
-        iframe.sendTouchEvent("touchend", [1], [10], [10], [2], [2],
+        iframe.sendTouchEvent("touchend", [1], [x], [y], [2], [2],
                               [20], [0.5], 1, 0);
         break;
       case "#touchend":
         ok(true, "Receive a touchend event.");
-        iframe.sendTouchEvent("touchcancel", [1], [10], [10], [2], [2],
+        iframe.sendTouchEvent("touchcancel", [1], [x], [y], [2], [2],
                               [20], [0.5], 1, 0);
         iframe.removeEventListener('mozbrowserlocationchange', onlocchange);
         SimpleTest.finish();
diff --git a/dom/interfaces/base/nsITabParent.idl b/dom/interfaces/base/nsITabParent.idl
index 5f1f59210b25..01c4fa1842bb 100644
--- a/dom/interfaces/base/nsITabParent.idl
+++ b/dom/interfaces/base/nsITabParent.idl
@@ -5,7 +5,7 @@
 
 #include "domstubs.idl"
 
-[scriptable, uuid(30361a5b-a3b8-4dbc-b464-e08761abb123)]
+[scriptable, uuid(b19038ba-0d75-40d2-be35-742e26d33bf9)]
 interface nsITabParent : nsISupports
 {
   void injectTouchEvent(in AString aType,
@@ -19,6 +19,8 @@ interface nsITabParent : nsISupports
                         in uint32_t count,
                         in long aModifiers);
 
+  void getChildProcessOffset(out int32_t aCssX, out int32_t aCssY);
+
   readonly attribute boolean useAsyncPanZoom;
 
   void setIsDocShellActive(in bool aIsActive);
diff --git a/dom/ipc/TabParent.cpp b/dom/ipc/TabParent.cpp
index 038c111620a4..e8b934eb08bf 100644
--- a/dom/ipc/TabParent.cpp
+++ b/dom/ipc/TabParent.cpp
@@ -1757,6 +1757,18 @@ TabParent::RecvEnableDisableCommands(const nsString& aAction,
   return true;
 }
 
+NS_IMETHODIMP
+TabParent::GetChildProcessOffset(int32_t* aOutCssX, int32_t* aOutCssY)
+{
+  NS_ENSURE_ARG(aOutCssX);
+  NS_ENSURE_ARG(aOutCssY);
+  CSSPoint offset = LayoutDevicePoint(GetChildProcessOffset())
+      * GetLayoutDeviceToCSSScale();
+  *aOutCssX = offset.x;
+  *aOutCssY = offset.y;
+  return NS_OK;
+}
+
 LayoutDeviceIntPoint
 TabParent::GetChildProcessOffset()
 {