When attempting to access the Twitch website in normal browsing mode, the page does not load properly. Instead of the site rendering, I only see a black screen with an infinite loading spinner. This issue does not occur in private browsing mode (incognito), Twitch loads normally there. Private browsing mode works correctly

Sounds like an add-on issue. Site works for me. see screenshot Are you running any security software besides MS Defender? Have you tried with Firefox in Troubleshoot Mode? https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode#w_how-to-start-firefox-in-4troubleshoot-modesf5safe-modesf

I have this problem too, twitch was working yesterday and I think firefox updated last night to 142.0 and now it just sits there loading forever, I tried troubleshoot mode and it still didn't work, only works in a private window.

clearing cookies and site data for twitch fixed it, hopefully its not a recurring problem.

I also have this problem. Clearing the cache helps but it comes back in about a week. I have tried Firefox with no addons and that doesn't help. Incognito and on Chrome also work so it's something about regular Firefox causing this to keep happening.