In case you don't find an answer and need to reinstall it, try uninstalling Firefox, delete your profile folder, then install Firefox again (take the latest version from their site). Your profile folder on XP is
C:\Documents and Settings\user name\Application Data\Mozilla
You will want to save your bookmarks BEFORE you do this. You can export them to a html file with the bookmarks manager. Just go to "Bookmarks", "Manage Bookmarks", "File" then "export"
Then when you are done reinstalling Firefox import your bookmarks back the same way. This usually clears up any problems that continue even after you uninstall and reinstall Firefox. You will have to reinstall your extensions if you have some installed.
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