The first three reports are hard to understand, but do seem to be related to memory in some manner. The fourth one is a hang in the Flash plugin, so that's probably not severe enough to cause a crash. Do you use Firebug a lot? If so, you might need to disable some of the built-in developer tools such as the debugger. In about:config, you can focus in on the most relevant preferences by typing or pasting '''devt*enab''' in the search bar above the list. If you rarely use Firebug, I would try disabling it on the Add-ons page for a while to see whether that makes any difference.