This could possibly be caused by one of your installed and enabled extensions (try IE Tab + 2.04).

Start Firefox in Safe Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Appearance
• do NOT click the "Refresh Firefox" button on the Safe Mode start window

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Use one of these to close Firefox if you are currently doing that by clicking the close X on the Firefox title bar.

• "3-bar" menu button -> Exit (Power button)
• Windows: File -> Exit
• Mac: Firefox -> Quit Firefox
• Linux: File -> Quit

IE Tab appears to have been the culprit.

Happened again. This time it killed all my tabs, pinned and otherwise. I had been running a flash idle game in an open window and apparently the new Firefox can't deal with flash very well anymore (which is highly aggravating), so it stopped responding entirely and so I closed it (by right-clicking on the . Then when I reopened it, it had lost all the tabs I had open, including the pinned ones, and only opened my home page. Of course, the option to restore the previous session was greyed out.

This is rapidly getting to the point where I'll simply abandon Firefox and move on if they can't keep their product stable and avoid this kind of crap. And yes, I do know that they apparently decided that they were no longer going to support a lot of 'legacy' stuff, which screwed a lot of people over. I moved to Firefox because IE was pulling the same kind of garbage (and was an unsecure browser), and if this keeps happening, I will have no problems whatsoever with tossing Firefox by the wayside and moving to something that doesn't break pretty regularly every few days.