5ef35728ff If there is a pending visual update `AsyncPanZoomController::NotifyLayersUpdated` will override scroll offset set from layout with the visual one. See [`visualScrollOffsetUpdated`](http://ffsearch.azurewebsites.net/#path=%2Fhome%2Fjoe%2Ffirefox%2Fgfx%2Flayers%2Fapz%2Fsrc%2FAsyncPanZoomController.cpp&line=4530) and its comment in the method.
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