By any chance, is your graphic card an AMD Radeon? I've been having problems with facebook too but there was a black screen not white one ;) For me, disabling hardware acceleration works but it's not really a solution since youtube videos etc are very slow then. To disable hardware acceleration go to options-advanced and uncheck "use hardware acceleration". Restart Firefox and see if it helps. If you do have an AMD GPU you can see here, I've just described similar problem with what I was able to find out for now. https://support.mozilla.org/en-US/questions/1081445