That likely because the user agent has Agency/92.8.2487.88 appended as you can see in the System Details.

• Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:99.0) Gecko/20100101 Firefox/99.0 Agency/92.8.2487.88

See also:

• https://support.mozilla.org/en-US/kb/how-reset-default-user-agent-firefox
• https://support.mozilla.org/en-US/kb/Finding+your+Firefox+version

Your User Agent shows: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:99.0) Gecko/20100101 Firefox/99.0 Agency/92.8.2487.88

Note the junk at the end.

https://support.mozilla.org/en-US/kb/how-reset-default-user-agent-firefox

http://www.howtogeek.com/113439/how-to-change-your-browsers-user-agent-without-installing-any-extensions/

Do you have enabled "Resist Fingerprinting" if you check ‘’’Resist Fingerprinting’’’ on the ‘’’about:config’’’ page as this affects the user agent?

• privacy.resistFingerprinting = false
• https://support.mozilla.org/en-US/kb/firefox-protection-against-fingerprinting

’’’Avast AntiTrack’’’ is also known to cause this issue.

This was a fresh install so no cache or history

This was a fresh install so no cache or history

Note the second reply by cor-el as your Firefox UserAgent is modified.

https://support.mozilla.org/en-US/questions/1375483#answer-1500954

Do you use Avast AntiTrack or AVG AntiTrack? They add stuff after your Firefox version that messes up website detection.

If not one of those, do you use any proxy server or spyware that modifies all your browsing requests?