Here's some info. https://support.mozilla.org/en-US/questions/1570225#answer-1807088

Why have I suddenly been denied access to web sites that I always visit?

The Firefox UserAgent you used to post this thread Mozilla/5.0 (Windows NT 6.2; Win64; x64; rv:109.0) Gecko/20100101 Firefox/115.0 as NT 6.2 is Windows 8.

Are you really using Windows 8 ? as most of the time I have seen threads of Firefox users on Windows 8 and not 7 or 8.1 was due to running Firefox in Windows 8 compatibility mode for some reason on Windows 10 or 11.

Firefox 116.0 and later requires Windows 10, 11 to run so if you download Firefox from Mozilla site with a UA showing you have Windows 8 then you would be served the Firefox 115 ESR.

This article show how to enable/disable compatibility mode on Windows 10/11. https://www.minitool.com/news/how-to-run-a-program-in-compatibility-mode.html

If you then do an internal Firefox update you will likely get updated to the current Firefox 140.8.0esr. If you prefer to have the current Firefox 148.0.2 Release then see https://www.firefox.com/download/all/

I can confirm that this is happening on windows 11 too. I have the current stable version. I can get to dells support page I enter a system ID and I get access denied. Some websites I can not get to at all. Just started with latest update Not happening with Chromium Version 133.0.6943.142 (Official Build) (64-bit).