Sorry to hear that chocomo99. Luckily Firefox regularly makes backups, so it might be possible to restore your tabs, by following the instructions at How to restore a browsing session from backup. (The sooner you do this, the more likely that the backup has not been deleted yet.)

If it never re-opens your tabs anymore, you might want to look at the section "Session didn’t restore correctly" here.

Vincent, Thanks for the reply. All the files in sessionrestore folder are over 3 years old. Maybe that would still work but I'm skeptical. Not to mention that I've closed and opened Firefox several times since the problem occurred. The real problem was that it never re-opens my tabs anymore so the "session didn't restore correctly" fix might work. However, after rebooting my computer the original tabs came back. Huh? Not sure how that worked but the problem is solved at least for now.