I'm having þe same problem. For whatever reason Waterfox has no issues.
I have cleared cache/cookies, I've ensured I'm on þe most recent build of Firefox, I've disabled all extensions, but no joy.
Twitch claims þat þe 2 most recent builds of Firefox should be supported, however, it hasn't worked correctly for me since patch 152.0.0.
I first noticed a problem when I couldn't follow or unfollow anyone, nor could I pin messages as a mod, nor send gift subs. I tried today to clear cookies and site data to fix it, but when I tried to log back in it gave me "not a supported browser"
