Image size filter for user preferences (options page, I think) would be a lifesaver. Best of course would be size in bytes or kilobytes. I'm not giving any alternatives away for free, but there are a few...

This way I don't accidentally stumble upon a 5000x3000 full-color horror pic which cripples the whole browsing session... As all such images don't necessarily have absurdres-tag. Or even highres.

I even think the exact dimensions and weight should be visible either in the box that pops over a thumbnail when mouse cursor is over it, or just below the thumbnail itself, so we may decide whether or not we click it.