Two things:
After deleting the unzipped directory, did you delete ~/.mozilla?
If you did not, try deleting it (when firefox is closed) and then reopening it
When you reopen it, launch it from a terminal window, this will output error messages there for you to get a better idea of the issue.
IF you still get the same error, try reinstalling firefox (after deleting ~/.mozilla), after looking on google it appears that it might be related to an old ~/.mozilla.
GL,
-Jason
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