how to upgrade firefox to window 11

There are no separate versions of Firefox for Windows 10 and Windows 11 as Firefox since 116.0 and later has requires Windows 10, 11 to run. If there are sites saying you are using Windows 10 then this is due to the NT 10.0 in web browser UserAgents as Windows 11 is basically based on NT 10.0 and Windows 10 is. There is no NT 11.0. A Firefox 154.0 UserAgent on Windows and 11 shows as Mozilla/5.0 (Windows '''NT 10.0'''; Win64; x64; rv:154.0) Gecko/20100101 Firefox/154.0