I have 298 tabs across 8 windows open right now and I can already tell firefox is about to crash at any moment. I go to about:memory and mash the buttons in the "free memory" box to buy some extra time, but eventually firefox goes down in flames and I lose all my open tabs. When it does finally crash Firefox can never restore my tabs, but I blame myself/my settings for that.
When things get to this point where I know firefox will die soon I end up bookmarking them all or even copying each URL into a text document with dreams that I'll go back to them after my browser has been closed and re-opened, but I almost never manage it. At least I have the option I guess and I know that if I ever do I'll find things that are of interest to me. There's just no shortage of other things that are of interest to me online so the newest stuff tends to win out.