I have a problem with Firefox Beta 52. It doesn't work in Firefox ESR 45, probably never worked. It seems to be implemented in bug 1235612. Sometimes audio indicator in tab is displayed for parts of the video that have no sound. It happens unpredictably, however, I noticed one specific scenario when it happens 1. Open attached video, play the video 2. While there's still sound, click in the center of timeline, then wait 4 seconds Result: audio indicator is displayed in tab Expected: no audio indicator, because second part of the video has no sound Audio indicator disappears on the second part of the video as expected, if I simply open video and play it.

If I pause the video, then continue it, sound indicator appears too. I assume there're a lot of similar scenarios in this bug. 1. Open attached video, play the video 2. While there's still sound, click in the center of timeline, pause the video, then wait 4 seconds 3. Play video

Too late for firefox 52, mass-wontfix.