Start Firefox in Safe Mode to Troubleshoot the issue and to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode
• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Thank you for the suggestion, tried it in safe mode, same behavior. Besides I don't really run any addons etc. I think I 'm just going to nuke it and reinstal

Your settings are not saved. try with new profile.

Create a new profile as a test to check if your current profile is causing the problems.
See Creating a profile:

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over the problem
Profile Backup and Restore

• http://kb.mozillazine.org/Profile_backup
• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

It would probably be wise to save all password records as a screenshot, because any method resetting them makes them inaccessible. You may also wish to save the pair of files involved, in case you find the cause of the fault and are able to use them again. The easiest method is to rename the files. That will also require you to setup a new master password (if used) and set up new logins.

• key3db & logins.json
  • Both are in the Firefox profile see:
    Profiles - Where Firefox stores your bookmarks, passwords and other user data_how-do-i-find-my-profile

See also

• http://kb.mozillazine.org/Password_Manager#Troubleshooting
• Usernames and passwords are not saved
• Where are my logins stored?

I keep separate backups of all my files so I was able to restore passwords from a backup. Apparently during the auto-update something got corrupted in either logins.json or keys3.db cause no amount of re-installing firefox over the existing files worked.