Description of problem:
After updating my system yesterday evening (to firefox-70.0.1-4.fc31.x86_64 and some other libs) i can no longer open dropdowns (like https://www.w3schools.com/tags/tryit.asp?filename=tryhtml_select) if the firefox window is on one of the external displays of my Lenovo P50.

Dropdowns work as they should if firefox is opened on the notebook display.


Version-Release number of selected component (if applicable):
firefox-70.0.1-4.fc31.x86_64

How reproducible:
always on my maschine.

Steps to Reproduce:
1. Open firefox
2. move it to 2nd or 3rd display
3. Click on dropdown element.

Actual results:
The dropdown does not open but it is showing the click "animation".

Expected results:
The dropdown opens.

Additional info:
Lenovo P50 - was updating to latest packets like 13 hours ago. System was working before that update as it should.