Hi, Is it [https://addons.mozilla.org/en-US/firefox/addon/bloomind-ft-sleekdark/ this]?? Please also see the section IMPORTANT ! (below About this Add-on). If the problem persists, you can also try to install this in a [https://support.mozilla.org/en-US/kb/Managing-profiles new profile] before installing other add-ons. If the new profile is okay, you can later [https://support.mozilla.org/en-US/kb/Recovering%20important%20data%20from%20an%20old%20profile?s=profile&r=1&e=sph&as=s copy the needed personal data] from the old profile and start using the new profile. You can then delete/troubleshoot the old profile. Firefox stores your personal data and settings in [http://kb.mozillazine.org/Profile_folder another location (profile folder)] separate from its [http://kb.mozillazine.org/Installation_directory folders/files]. A new profile would have the default Firefox settings in '''Tools''' ('''Alt''' + '''T''') > [https://support.mozilla.org/en-US/kb/Options%20window Options] and [http://kb.mozillazine.org/About:config about:config], and usually would also be empty of '''Extensions''' and themes ('''Appearance''') in '''Tools''' > '''Add-ons''', and their settings. Also, a new profile would have no previous stored website cache/cookies/data/preferences: '''Tools''' > [https://support.mozilla.org/en-US/kb/Clear%20Recent%20History '''Clear Recent History''']. [https://support.mozilla.org/en-US/kb/Profiles?s=profile&r=2&e=sph&as=s Profiles Howto] [http://kb.mozillazine.org/Profile_folder_-_Firefox Profile Folder & Files] [http://kb.mozillazine.org/About:config_entries about:config Entries]