Just load the UDKGame-Browser-Shipping-Sanctuary.html AR: After the loading is complete, just before showing the "Unreal" logo - black screen over the game area. Switching focus to another window and back solves the problem, the black screen disappears. Mac OS X 10.6 specific. OS X 10.7, 10.8, 10.9 work fine. Reproducible on FF 25, 26. FF 27, 28 work fine.
Doesn't sound like a JS issue. Tentatively guessing graphics.
Don't really care about bugs on 10.6; small user base, unlikely to be running bleeding edge content. This is likely some WebGL feature that 10.6 gfx drivers handle buggily (there are a bunch). We'll hopefully stop supporting 10.6 at some point soon anyway.
Whiteboard: [games:p?] → [games:p-]
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