Simply put, cannot connect to Sync from Firefox (Windows). I can sign in just fine into the Mozilla account (that's how I'm writing the question, after all). However, when I try to sign into Sync it asks for a password, then for an authorization code and then fails with "'''Bad Request''': ''Something went wrong. Please close this tab and try again.''" Tried it multiple times, even in Troubleshoot Mode, got the latest Firefox and all, but this seems like a communication issue, not a browser issue.