I'm running Ubuntu, and every once in a while, I boot up my PC and some app is missing that was there previously. Last night I shut down my computer, and this morning Firefox was missing. I lost all my browsing history, cookies, bookmarks, extensions, etc.

This has happened several times before. Does anyone know what's going on? I know I'm not personally removing any of these apps. Is there something I could be doing unknowingly to do this?