Hi,
Please check if this happens in a new profile. If the new profile is okay, you can later copy the needed personal data from the old profile. Firefox stores your personal data and settings in another location (profile folder) separate from its files/folder. A new profile would have the default Firefox settings in Tools (Alt + T) > Options and 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 etc., (Tools > Clear Recent History).
Profiles Howto
Profile Folder & Files
about:config Entries
Hi,
Please check if this happens in a [https://support.mozilla.org/en-US/kb/Managing-profiles new profile]. 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. 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 files/folder]. 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 etc., ('''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]
