The browsers are fixing this; no plugins should be needed.

Is there actually a legitimate use for 0x0 iFrames that can't be easily replicated some other way? Why do we allow them?

Where do you draw the line? 0x0 doesn't work. Let's use 1x1 and blend it in somewhere. 10x10? Probably can find a square somewhere to hide it. Or a long rectangle at the bottom perhaps with a solid color. I don't see blocking 0x0 as a real solution to the problem.

Same problem with setting the position off screen or 0% opacity. There is a lot of ways to hide an iframe

Ajax file uploading - http://www.sortfolio.com/signup