Hello, is anyone able to help me? Firefox is basically unusable right now.

try disabling add-ons, adjusting privacy settings, ensuring Firefox is up-to-date, testing in a new profile or private window, and checking site permissions. If none of that works you could always try to restart your device.

Hey we've been tracking this issue since you first reported it and a few people besides you reported it too. So you definitely are not alone on this.

I was waiting for a definite answer before responding to you since you already tried clearing cookies and browsing data, refreshed Firefox, and uninstalled and then reinstalled Firefox.

But the strange thing is, I've seen at 4 people say clearing "Cookies and Site data" erases all of Google's cookies and fixes the problem. Even though it looks like you already did that. So I kept digging for a nerdy answer and I found out that it looks like Google is setting cookies incorrectly when you try to login and it duplicates those cookies.

Here's proof one user was able to fix it by erasing all of Google's cookies: https://support.mozilla.org/en-US/questions/1469214#answer-1681555

So as long as those bad cookies from Google are there, it will always block you from signing in. So what I propose is that we go back to the Settings area of Firefox and keep clearing all the cookies until there aren't any left. Or we erase all the Google ones only. If that still doesn't work, then we should clear all the cookies and site data.

See: https://support.mozilla.org/en-US/kb/clear-cookies-and-site-data-firefox#w_clear-cookies-for-any-website

And if this problem is still there, I'd say we go straight to the file holding all the cookies (cookies.sqlite) and erase it completely. Or before deleting the cookies.sqlite file, copy it to another folder like My Documents so a Firefox developer can inspect it very closely to see what the hell is going on.