When I am browsing the internet, a black rectangular appears at random, mostly when I am watching videos.
When zooming in and out, the black box appears frequently and display flickers.
Most importantly, it is also visible in Firefox settings.
It appears in the address bar and randomly appears when loading YouTube videos and scrolling through YouTube videos.
When I move my mouse over the black box, it disappears.
Create a new user on your machine, and then try again triggering the black box and flickering.
It could be caused by one of the many extensions that you have installed.
You could also try a new FF profile to narrow down the problem.
Have you checked the logs to see if something appears there?
I’ve created a new profile from about:profiles and lunching the browser from new profile still has the issue.
The problem was not resolved by disabling all extensions, starting the browser in safe mode, or refreshing the browser by about:support.
Nothing is logged i checked the logs from about:logging
Create a new user (system, not FF) and see if the problem persists.
Also take a look at system logs.
black box shows up randomly in firefox at new user also but it seems to solve the flickering issue.
log from journalctl -b | grep “firefox” pastebin