sgt pepper

I just remembered that i had CCleaner on my computer so i decided to give it a run to free up some space on my computer. well after i ran the cleaner, alot of webpages fonts and just the way they look are alot different, like on ebay and myspace. But this is only happening on mozilla firefox and not when i use IE. can anybody help me to get this back to the way it was or just help me figure out what happened? thanks