All versions of IE (including 10) appear to hold on to a significant amount of memory allocated by iframes until window.top.unload occurs. This creates quite the challenge f
In IE 11, just setting iframe.src = 'about:blank' seems to fix this. Otherwise, you can watch the memory grow forever in the F12 Memory tab, even if you're removing iframes from the DOM and letting them be garbage collected. If you blank the iframes first, you see the memory go up and down as you'd expect.