I'm not sure if uninstalling Firefox will clear the profile - if not, reinstalling will just bring the same problem back.

You can clear your profile by deleting (or renaming/moving, in case you want to recover it) the following two directories:
C:\Users\<your user name>\AppData\Local\Mozilla\Firefox\Profiles\<some long string of characters>.default
and
C:\Users\<your user name>\AppData\Roaming\Mozilla\Firefox\Profiles\<the same long string of characters>.default

(Path will be slightly different on XP, which I haven't used in enough years I can't remember exactly -- under "Documents and Settings" rather than Users?)

Firefox also has a "safe mode" which can sometimes be helpful:
https://support.mozilla.org/en-US/kb...sing-safe-mode