Will it not delete ? If not need to do Right Click then Properties and change the permissions. You may have to reboot. For new Permissions to take effect. If it will not do what you want and do not want to waste time on it https://www.malwarebytes.com/fileassassin/ this will help. Also maybe in Windows Safe Mode. I would think delete from the Dos Prompt would work also. Since is corrupted..... fyi : Most people with XP are using 52.5.0 ESR. It will continue to get security updates until May 2018, and you can download and install it from this page: https://www.mozilla.org/en-US/firefox/organizations/all/ <b>Note : Legacy Extensions will be deleted or removed in any version update after May 2018</b>. You should make a backup of your Profile before going back and just because: https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles Please let us know if this solved your issue or if need further assistance.