I'm curious if it will be possible to get this feature working in Firefox. Since other posts here indicate that this was possible for Flash because it is using the Pepper stack and since Firefox has said they do not plan to adopt Pepper (https://bugzilla.mozilla.org/show_bug.cgi?id=729481), I wonder how possible this will be.
This feature could significantly negatively affect Firefox's market share.
Shumway is a more direct route to solving this problem than reverse engineering the Pepper API. The Shumway approach has several other advantages too, such as portability and unifying the graphics/audio/JIT stacks of the browser and Flash. Assuming Shumway works out (that's a big assumption, but so is assuming that Pepper could be reverse engineered and shipped), I don't see any technical obstacles to Firefox doing this as well.
The bug indeed seems to conclude it's impossible until Flash is eradicated, though disabling Flash in anything but the foreground tab + click to play will probably make it moot. (Apparently Safari does exactly this)
There's alternatives such as Shumway.
Also, in my experience lack of Flash or it crashing is seen as a way bigger problem than nasty tabs, as of now.
This feature could significantly negatively affect Firefox's market share.