The loot screen is not doing anything on its own. I can toggle between windowed and full screen mode to advance it a couple of frames each time, but that's it. I can't inspect the loot I received. This has also happened to me in other places as well, including in game, where it causes me to lose, and in the multiplayer area, but most of the time it's just the loot screen. This started about a week or so ago, and occurs in both Firefox and Chrome. Edit: This doesn't happen all the time, but it happens often enough.
That's really strange. I haven't experienced this before either. Can you try clearing the cache on the browser and possibly re-installing flash? I can't even think of what might be causing the issue, especially if it's intermittent...