Frequently after my computer comes out of sleep mode or hibernation with Firefox still running, I will try to input text (anywhere in the window) or push the volume buttons on my keyboard and it causes the program to not respond. The only option is to close and restart it, but it doesn't remember my tabs anymore, nor does it remember closing my tabs (when I look for them in the 'recently closed tabs' menu). Often this does not solve the problem, and I end up having to restart my computer for it to work again.