Firefox says you’re on outdated/unsupported version of the browser !

[Gt-truth]

Latest version is already installed , however when i want to upload an a video file to the YouTube then it says this

Quote

Improve your experience
You are using an unsupported browser or an old browser version that may cause YouTube Studio to be slow or unreliable. Try the latest version of one of these instead.

here is a screenshot

[AdvancedSetup]

Perhaps one of your other extensions is confusing YouTube?

Try restarting Firefox in Troubleshoot Mode and see if YouTube still complains

 

Edited July 1, 2021 by AdvancedSetup
updated information

[Gt-truth]

Most likely one of the extension behind the issue . will check which one .

Restarting Firefox in Troubleshoot mode and the problem is gone (I made this reply with Firefox switch to Troubleshoot mode)