The issue is that the plugin model means that Firefox has no way of knowing if sound is playing via a plugin. The plugins access the OS's sound layer directly.
The objection [from the bug report] being that they don't want to introduce inconsistent behaviour depending on how the sound is being played (plugin vs HTML5 audio).
In modern browsers it's possible for a webpage to change its favicon dynamically. Developers should take the habit of indicating their site is playing sound there.
True... It would still be a useful good practice for non-annoying websites. Sometimes you start a video somewhere but can't remember in which tab it is.
