I often use Restore Previous Session to get back all the tabs (5-15) I was using. The last two times I clicked it, Firefox immediately shut down, and then when I opened up, the 'Restore Previous Session' option was greyed out. The first time, I was able to find the sites again on "Show All History," but the second time, it had wiped out my WHOLE history. What's going wrong? What can I do to fix it? I know nothing about the inner workings of computers. Nothing.