Same issue, came looking for a solution, tried all of the above too, to no avail.
When I go to chatgpt .com and click on “Log in”, nothing whatsoever happens. Even the left, animated side of the homepage is missing. The whole thing’s just completely dead in Firefox (115.15.0esr (64-bit)).
I can log in using Opera (85.0.4341.22), but the UI stays blank except for the three buttons at the top, same as it was in Firefox before I cleared the cache/cookies etc. to try again. When I click on “New chat”, nothing happens.
It works in Chrome (Version 109.0.5414.120 (Official Build) (64-bit) … I know … 
).