Comment 5 for bug 582640

If I'm understanding you correctly, you need to scroll down to the buttons on the Restore screen because you had a _lot_ of tabs open? Maybe too many for 512 Mb RAM? When RAM is full your swap partition should be used but if that gets full too then you might have a (crashing) problem. What does the Resources tab of System Monitor (under System -> Administration) show? Or it could be that one of the tabs has a page with a bad piece of Javascript, causing Firefox to crash.

To get out of the Restore cycle you describe, as soon as you have successfully restored a browsing session, close Firefox before it crashes again. You will be asked if you want to save all your open tabs, I recommend saying "no", but even saying "yes" should result in your next Firefox launch working better than an automatic restore, although it might crash again after that depending on number of tabs open and/or a bad piece of Javascript on a page in one particular tab.