Does that mean that using Microsoft's license doesn't cover users of the H.264 codec in Windows 7?
What if Firefox runs Windows Media Player or Flash player in an hidden window (or equivalent hack) and extracts the frames?
What if Firefox automatically downloads ffdshow but doesn't ship it?
What if Firefox automatically downloads a Windows 7 update for Windows Media Player and/or the Microsoft H.264 codec, extracts the binaries from it and runs it on Windows XP via suitable hacks?
Some legal investigation of these things seems quite essential, especially since 6 million dollars per year for H.264 licensing are a significant portion of Mozilla's 43 million income that Wikipedia reports.