UPDATE 2: I found it - when you run out of disk space, OneTab freezes, becomes completely unresponsive, doesn't save new links and doesn't open already saved ones. And most importantly: AFTER FIREFOX RESTART, IT DELETES ALL SAVED LINKS !!!

UPDATE: Today it deleted all OneTab data again when I had not enough free disk space. (I learned my lesson first time, I always back it up). It's not robust. Beware of that.

It works well. But I already have lost all my data (about a thousand links) in OneTab once.

Onetab is NOT a backup tool !!

Fortunately, it has a great import/export function that is very easy to create backups. So use it! Don't make same mistake as I did.