Bug 855916 Add a debug pref which allows moz gesture events through content r=jimm

browser/app/profile/firefox.js

@@ -1232,3 +1232,6 @@ pref("plain_text.wrap_long_lines", true);
 pref("media.webaudio.enabled", true);
 #endif
 
+// If this turns true, Moz*Gesture events are not called stopPropagation()
+// before content.
+pref("dom.debug.propagate_gesture_events_through_content", false);

browser/base/content/browser.js

@@ -768,7 +768,10 @@ let gGestureSupport = {
    *        The gesture event to handle
    */
   handleEvent: function GS_handleEvent(aEvent) {
-    aEvent.stopPropagation();
+    if (!Services.prefs.getBoolPref(
+           "dom.debug.propagate_gesture_events_through_content")) {
+      aEvent.stopPropagation();
+    }
 
     // Create a preference object with some defaults
     let def = function(aThreshold, aLatched)