Yeah, I have browser addon. Disabling or removing it does not help. Other browsers I have tested on Bluefin, e.g., Zen, Florp, Brave, Firedragon, Edge, Chrome - all have the same issues and error message.
When you try to login with bogus credentials, it’s expected to get “This username does not exist” error on twitch and not the one I posted. Using my real credentials produce the same error
My third PC (Arch) is on the same network and copying my FF profile from Bluefin works fine there. Same when I test with Mint (VM).
Did you try to enable dns-over-https in firefox to see if it works when you use that? That way you can rule out if something blocks the request on dns level. It seems very odd that all browsers have the same problem, that should almost indicate some network level setting.
Anyhow, works fine for me… hope you will figure it out what causing this.
I used DoH Max protection with Cloudflare and NextDNS to no avail.
I found one similar topic for Vivaldi for Windows, last active 2 days ago, but not sure if it will be OK to put the link here. On their forum there is no solution either.
At the moment, I will be using the Arch PC to access twitch when I want to be more active there.