Firefox crashes unexpectedly and without warning during use. There seems to be no active "trigger" for the crash i.e. not from a specific page loading, action by the user, plugin that is loaded. The crashes occur anywhere between 3 hours and 24 hours of use which leaves plenty of time to load and reload pages successfully, but every now and then, kapoof! The crashes occur when Firefox is actively or not actively being used (more commonly, when the browser is idle, in the background, or when the user is away from the computer and it is locked).