I came here with this same issue, and it just started the last time Firefox updated. It also happens for me on Home Depot. I have no idea what is causing this or how to fix it, except that all the suggested things I came up with after google searching, did not work. This is a screen shot of my screen. I use these sites all the time, and at a loss with out them, I'm so frustrated. EDIT to say, I am using windows 7, if that matters.