I'd just reformatted my laptop and installed a fresh copy of the latest firefox. Then, I found that things weren't right as it keeps lagging/freezing and crashes from time to time especially when you're opening a few new tabs at once. Since the previous firefox worked fine, I thought it might be the latest version having problems, so I downloaded the older version and even upgraded to the current 20.0 beta but all failed! Right now, I have no clue if it's the problem of my computer or firefox itself. Other browsers worked perfectly fine chrome etc except firefox.