If you have resist fingerprint on, or use Librewolf, then you need to disable resist fingerprint, clear twitch cache and cookies then restart firefox/librewolf. Go back to twitch, log in (remember me for 30 days), and you should pass twitch’s integrity check on login and be through.
Disable ad-blocking/tracking extensions - uBlock Origin, Decentraleyes, TTV Pro LOL etc. (sometimes I need to do this for twitch integrity check to pass. This should only happen once during the authentication request).
Clear cookies and site data (via lock symbol on the left-side of the URL bar)
If you have resist fingerprint on, or use Librewolf, then you need to disable resist fingerprint, clear twitch cache and cookies then restart firefox/librewolf. Go back to twitch, log in (remember me for 30 days), and you should pass twitch’s integrity check on login and be through.
This is what I do with my setup on Librewolf:
oh, yes I have resist finger printing on.