On my desk top

You just can't trust that Windows compatibility reporter.

Is there a particular problem you were trying solve with your Firefox?

Shut down Firefox. Using your file browser, open the Programs Folder on your computer.

Windows: C:\Program Files C:\Program Files (x86) Note: Check Both Folders

Right click on Firefox.exe and select Properties. Now select Compatibility. Turn Off Run This Program In Compatibility Mode, and Run This Program As An Administrator.

Do the same for any Firefox shortcuts you have. Now restart Firefox.

ran trouble shooting on fire fox and it says it's not compatible because i use windows 10, when it only uses windows 8 and windows vista!

The desktop Firefox web browser has not supported the old EOL Windows Vista since 52.9.0 as Windows 7 or later has been the requirement since.

from https://www.mozilla.org/firefox/99.0/system-requirements/ Windows Operating Systems (32-bit and 64-bit) Windows 7 Windows 8 Windows 10 Windows 11

Windows 8 mention includes 8.1.