I had the same problem as Op.

for over a year i couldnt log into my twitch account cause it kept pissing and moaning about my browser not being supported, despite being on a supported version and browser.

persisted through reformats, through LiveCD tryouts, different physical computers, browser resets/reinstalls, and with all addons uninstalled and/or disabled.

Only recently started working again for some reason.

I'd wager twitch is just shit at shit.

thank god I wasnt a streamer wasnt financially dependent on it.