Weirdness! Screenshot of another website overlays all crossbrowsertesting.com pages except the homepage

I don't know what's going on, when I log in, I can see the normal page but any link I click on brings me to a page with an overlay image of another website (in this case, istockphoto.com's buy credits page) and I can't do anything to get rid of it. I'm using Safari on Mac (latest everything) and I've tried clearing the cache, tried restarting Safari, and nothing works. The overlay is darker, not full opacity, and if I resize the window, I can see crossbrowsertesting is underneath it, but I just can't access anything.

I had to go back to using Firefox, which for some reason, Crossbrowsertesting.com support told me not to use since I'm on a mac (due to issues last year).

Anyone ever have this problem before? This only started today. I have not visited the istockphoto buy credits page in a long long while, so I don't know how or why it's showing that instead of crossbrowsertesting.