This has happened to me a few times too. Try clicking the button I circled out in the attachment below. It should do the trick if we've encountered the same problem.
I have Firefox 5.0, and I haven't been downloading any extensions. Don't even know what that would be. This problem has only occured like twice or something to me. Maybe it was even on another computer xD I don't know.
I had to whitelist this page to see that picture, Levian, but I was interested in finding out what button that was. That button solves the problem. Thanks.
It's set to block ads. It thought your image was an ad because of its filename. Thanks to Adblock, I will never see another ad on the internet again. I'm surprised they haven't made it a law that all browsers have it installed.