Bman,
FireFox and gmail working here.
I had your problem a few years ago (with gmail, that is

). If I remember, it was a gmail file that was corrupted. Seems like maybe a profile. There was not much help from gmail. They have forums that you ask questions on, and I never got helpful answers or, sometimes, even replies. Again, a few years ago.
Seems like I finally corrected by deleting gmail completely, reinstalling and setting up a new email account. I used the same id and password, and everything worked. I tried the setting up new account, but still had the problem until I uninstalled and reinstalled gmail.
Of course, the problem was I lost all contacts, birthdays, stored (local) emails, etc. My pc died about six months ago, and on the forums again, I got no help to get to my contacts, birthdays, etc. The motherboard died, but I still had the hardrive, and access to it, but could not find the correct files to get the lost data I wanted.
The lack of help/responses could have been because of my Texas accent

. You might have better luck!