Could you confirm you're having issues using mobile Firefox iOS? (The technical data attached would hint at desktop version on unsupported Windows 8 — so please clarify if that's not the case.)

I am using a desktop computer which runs Windows 11. I am using the most recent version of Mozilla Firefox.

Unless you're posting from a different device, or are using user agent scrambling addons or settings, you're on a very old, legacy version — that shows even an old, unsupported Windows.

The most simple reason would be somebody configured the system to run Firefox in Windows 8 compatibility mode when there is no reason to. See the steps in a similar thread: https://support.mozilla.org/questions/1552694

(Once you're not running in legacy mode, it will start updating itself over time — it will take your from 115 ESR to 128 ESR to 140 ESR that should not have any compatibility issues with any big site operators… You can later migrate to normal, rapid release version that ships more often.)

I found that my Firefox was checked to use the compatiblity mode for Windows 8. I unchecked that box and my Mozzilla Firefox updated to a more recent version, (Version 140.11.0esr). I opened Firefox but it still would not allow me to sign in to Amazon. I get the Amazon homepage quickly but when I click to sign in nothing happens. Any suggestions?

It might take some time for their session/account fingerprinting to adjust to your new browser and expire any stale data they might have saved with you.

I'd try logging in via Private Window, which should give you a clean start with them, or Clear cookies and site data in Firefox either for that site, or for some recent time frame, or maybe even going to the list of data stored and remove anything that sounds like coming from any Amazon host or their partner.