Hi, sorry no idea why. Please grab a copy of your Profile :

• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

Please Refresh but do this 1st: Delete your Cookies and Cache and TEST.

• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

then

• https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings

TEST....... If no issues then Extensions which need to be added back in 1 at a time and tested ..... Or it is your Profile : Make a new one and test ...:

• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

If is your Profile :

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile
• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

Note: Any customization will revert back to default, you will also need to reinstall Extensions.

Please let us know if this solved your issue or if need further assistance.

Two footnotes:

(1) If you have a lot of bookmarks, export and backup may be very slow.

(2) I have a page that can convert a .json/.jsonlz4 backup file to a .html export file if you want to try that.

https://www.jeffersonscher.com/res/bookbackreader.html

The automatic backups are stored in your profile folder, in the bookmarkbackups folder. See: Profiles - Where Firefox stores your bookmarks, passwords and other user data.

You can check for problems with the places.sqlite database (bookmarks and history) in the Firefox profile folder.

• use "Verify Integrity" on the "Help -> Troubleshooting Information" (about:support) page

See also:

• http://kb.mozillazine.org/Locked_or_damaged_places.sqlite
• https://support.mozilla.org/en-US/kb/Bookmarks+not+saved#w_fix-the-bookmarks-file