First quit your current Firefox by closing the program completely, then you are able to finish an install of Firefox again. Let me know if this helps.

As to your account, I called for more help.

HI tombtomb, I understand that you created an account with Firefox. First, can you clarify if this is an account in support.mozilla.org, accounts.firefox.com or another site?

I can recommend that all of the information on your local profile will have all of the information that was synced when you created the Firefox account if it was a Firefox account. I've lost my Firefox Sync account information - What to do