http://kb.mozillazine.org/Uninstalling_Firefox

Try to clear the cache and cookies. To clear cache and cookies do the following: #Go to Firefox > History > Clear recent history or (if no Firefox button is shown) go to Tools > Clear recent history. #Under "Time range to clear", select "Everything". #Now, click the arrow next to Details to toggle the Details list active. #From the details list, check ''Cache'' and ''Cookies'' and uncheck everything else. #Now click the ''Clear now'' button. Further information can be found in the [[Clear your cache, history and other personal information in Firefox]] article.