Created attachment 840051 [details]
video with the bug

This started happening after updating from firefox 77 to 78.

Clicking on tabs and scroll bar sometimes doesn't work.
I click and nothing happens until I move the mouse.
This seem to happen only on the edge of the screen (I have the title bar
disabled).

I tried with the version from mozilla.org and I couldn't reproduce it.
I also tested on Wayland and I couldn't reproduce it there either, didn't try
for to long since switching tabs was pretty slow.
I'm using mouse gestures on Plasma and the problem manifested with mouse
gestures enabled as well as disabled.

Operating System: openSUSE Tumbleweed 20200724
KDE Plasma Version: 5.19.3
KDE Frameworks Version: 5.72.0
Qt Version: 5.15.0
Kernel Version: 5.7.9-1-default
OS Type: 64-bit