Every firefox and window is blank white. Completely featureless below the top margin of the window, including tabs (no individual tab lines are visible). The top margin itself is black and featureless except for the three red, yellow, and green buttons for closing, minimising and maximizing the window. If I right click I get the usual "Open new window, Open new tab,..." menu. The cursor changes from arrow to pointy finger to text insert symbol as I scroll over the blank page. If I click and hold on the black top margin and move the window I get a small thumbnail image of the page I should be on, the firefox start page for example or the Preferences page if I have selected it from the top menu. Because of this, the usual advice to troubleshoot via Preferences is useless. As I have been messing around trying to fix this Firefox has crashed and frozen frequently. I restarted Firefox in Safe mode and the small Safe mode window was likewise blink white but the top margin was not black, and I was able to click the blank window where "Restart in safe mode" should have been, which did open firefox, I assume in safe mode, but the situation was the same. I deleted and reinstalled Firefox but the situation was the same. This is all on a 2008 MacBook Pro running Yosemite. The problem started while someone who isn't me was streaming content on a European Hotel Wifi so I suppose malware suspicions are high. The streaming content froze my system and the laptop had to be manually shut down. Also having a problem in my Finder in that the Search and Spotlight Search are turning up zero results which I assume is related. Safari no problem (typing this on same machine). No other programs effected. I tried to attach a screen grab of the Firefox window and, just to make things more peculiar, on jpg or tiff, the upper margin which is black in Firefox appears as white in the screen grab, whether grabbed by window or by selection.