Created attachment 1548701 [details]
Menu displacement

Description of problem:
Firefox on Wayland is rendering context/pop up menus at the wrong position if the scale is set to something different then 1x.

I think Firefox is not correctly getting its size and thinks its only 1/4 as big as it is, because as long as you open a context menu in the top left quadrant everything is normal, but if you're opening one outside of that bound the menu gets rendered in that top left quadrant and it behaves like the screen is only that size.


Version-Release number of selected component (if applicable):
Firefox 66.0.1

How reproducible:
Always

Steps to Reproduce:
1. Set scaling factor to something else then 1x
2. Open Firefox
3. Right click anywhere or open the menu

Actual results:
Menus are placed incorrectly and context menus are sometimes unclickable.

Expected results:
All menus should open at the correct position

Additional info:
I'm using a 125% scaling factor but it also happened when setting to 2x.