It’s because Twitch tries to fingerprint your browser as part of the login flow.
You can set resistFingerprinting to 0 and then Firefox should work. User agent switching doesn’t work.
Edit: alternatively, open about:config, set privacy.resistFingerprinting.exemptedDomains to *.twitch.tv. This will disable fingerprinting protection for Twitch, making the login work at the cost of privacy protection without disabling it everywhere.
Also, any plugin that Twitch doesn’t like (for example TTV LOL) is detected and will prevent a log in. You’ll need to disable the plugin to login, but can use it after logging in.
It’s because Twitch tries to fingerprint your browser as part of the login flow.
You can set
resistFingerprintingto 0 and then Firefox should work. User agent switching doesn’t work.Edit: alternatively, open
about:config, setprivacy.resistFingerprinting.exemptedDomainsto*.twitch.tv. This will disable fingerprinting protection for Twitch, making the login work at the cost of privacy protection without disabling it everywhere.This worked for me, but for OP: don’t forget to enable it back on after login. It’s not required to watch Twitch, only for ‘the first’ login.
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Also, any plugin that Twitch doesn’t like (for example TTV LOL) is detected and will prevent a log in. You’ll need to disable the plugin to login, but can use it after logging in.