The Firefox UserAgent you used to post this forum thread with is Mozilla/5.0 (Windows '''NT 6.2'''; Win64; x64; rv:109.0) Gecko/20100101 Firefox/115.0 The NT 6.2 is Windows 8. Either you have modified your UserAgent to be this or the more likely case is you are running Firefox in Windows 8 compatibility mode for some reason which can explain why you are using Firefox 115 ESR as Fx 116.0 and later requires Windows 10, 11 to run. By running Firefox in Windows 8 compatibility mode, when you download Firefox on mozilla.org you would get served Firefox 115 ESR and not the current Release. If your UA is modified https://support.mozilla.org/en-US/kb/how-reset-default-user-agent-firefox Or you can undo the running Firefox in Windows 8 compatibility mode as there are guilds around like https://www.minitool.com/news/how-to-run-a-program-in-compatibility-mode.html