Hi, You can try deleting the [http://kb.mozillazine.org/MimeTypes.rdf mimeTypes.rdf] file in the [http://kb.mozillazine.org/Profile_folder Firefox Profile Folder] after exiting Firefox. To open the profile folder via Firefox: '''Help''' ('''Alt''' + '''H''') > '''Troubleshooting Information''' > '''Show Folder'''. [http://kb.mozillazine.org/Profile_folder_-_Firefox Firefox Profile Folder & Files] If the problem persists, please try to [https://support.mozilla.org/en-US/kb/reset-firefox-easily-fix-most-problems Reset Firefox] via '''Help''' ('''Alt''' + '''H''') > '''Troubleshooting Information'''. (To revert to the previous profile you were using, close the new profile (i.e. exit Firefox), start Firefox and choose the '''Default User''' profile. While the [https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles Profile Manager] is open, you can also delete the newly reset profile (the one containing random numbers), or the former profile, as the case may be). If the reset is okay, it would be a good idea to delete the old profile as otherwise it would be left intact with the previous data/cache until deleted. [https://support.mozilla.org/en-US/kb/Managing-profiles Managing profiles] [https://support.mozilla.org/en-US/kb/Profiles?s=profile&r=2&e=sph&as=s Profiles Howto]