Chrome did it to me too. I had many links saved in onetab that are now lost. No software is completely stable on all computers in all situations.
Did you double-check your profile folder? Firefox might have created a new profile for you while leaving the old profile there. If you're on Linux or Mac, try typing this in a terminal:
firefox -ProfileManager -no-remote &
Then, if there is more than one profile listed there, try each one to see if it's the old profile.
(I'm not sure how to find the profile folder on Windows.)
