There is another bug about this issue. I had already uploaded a patch for it: https://bugzilla.mozilla.org/show_bug.cgi?id=831890. There are two issue creating it. One is APZ, another is our fault of code. One of the patch of these two issues may fix it. The APZ bug had been created: https://bugzilla.mozilla.org/show_bug.cgi?id=961636. I had put the patch of it at bug 831890. Please sync up with those two bugs.