I faced a similar issue once it usually happens when the Firefox profile or Sync doesn’t load properly. Try restoring from an automatic backup via Bookmarks → Import & Backup → Restore. This thread might also help: [https://support.mozilla.org/en-US/questions/1283341 https://support.mozilla.org/en-US/][https://realestateagentslondon.co.uk/ visit site][https://support.mozilla.org/en-US/questions/1283341 questions/1283341].