Strange image distortion on icloud.com

I see this every time I access icloud online (even seeing that screen when I log out of email). It just happens for a moment, then goes away and the screen looks like it normally should. It started a few months ago and I didn't think anything of it, but I want to make sure it's just an image/Java glitch and not something more serious. Anyone know what that is?

I'm using Firefox 37.0.2 (newest version) and I keep my Macbook Pro up to date.

It's worth noting that I just tried this on a Windows laptop running 7 with up to date Firefox and it doesn't do it on that, though icloud takes forever to load on there.