First, my response is not a solution; but others may be able to help if you give more details, like: 1. Which version of Firefox are you using? 2. How many days of browsing History did you set Firefox to remember? 3. What OS are you using? Just to say, the same thing has happened to me (occasionally) with each version of Firefox since version 2 and up. (I'm using Windows XP). During those times, I had my FF history set to remember at least 90 days of visits. I noticed that the lower the number of days I entered in that history preference, the less frequently I lost my history. That occurrence has not repeated itself since almost a year ago, when I set the history to remember no more than "at least 7 days". (I don't propose this as a solution, though, since FF should be able to retain as many days of history as that preference allow). I do wonder, though, if there is a connection between the amount of data stored and FF's tendency to 'purge' itself.