I'm not sure this is a CCleaner issue (great product), but rather an issue related to a corrupted FireFox cookie file. That is why the reinstall may have helped Faiakes. I'm not certain, but I found this solution and it solved the issue for me.
However, credit should be given to "stockbridge" at YahooAnswers (http://answers.yahoo.com/question/index?qi...01132814AAkPXWD).
Good luck.
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1. Look in your profile folder (http://support.mozilla.com/en-US/kb/Profil...nd_your_profile) for a file called "cookies.sqlite" (make sure you have it show "Hidden and System files").
2. Close Firefox and delete this file (or just rename it to like cookies_OLD.sqlite so you have the original).
3. Re-open FireFox and it'll create a new, non-corrupted file.
From here on out, the cookies should behave normally.
Source(s):
http://support.mozilla.com/tiki-view_forum...5&forumId=1