As per these threads: https://support.mozilla.org/en-US/questions/1018583?esab=a&as=aaq#question-reply https://support.mozilla.org/en-US/questions/1018244?esab=a&as=aaq https://support.mozilla.org/en-US/questions/1004248?esab=a&as=aaq There is a conflict with the Ghostery add-on and Firefox 31 or subsequent versions that causes the options window to appear totally blank, along with the Clear Recent History window. Screenshots: http://i62.tinypic.com/2iiy4jp.jpg http://i60.tinypic.com/xo1cp2.jpg Other windows, like add-on preferences windows, the print window and the bookmarks window all display normally. Is there any way to remedy this? Right now the workaround is to keep Ghostery enabled, disable it when you need to change certain options or clear your browser's cache/history and then re-enable it. As Ghostery is an invaluable add-on, I would rather keep it enabled 24/7.