[Affected versions]:
Nightly 66.0a1

[Affected platforms]:
Platforms: Windows

[Steps to reproduce]:

1. Open the Firefox browser and reach Youtube.com and play any video.
2. Reach https://www.esoui.com/downloads/info2099-TheElderBar.html in a second tab and play the video on the right with sound.
3. Mute and Pause the video from the second tab.
4. Reach the first tab and use the volume button or stop and play the video.
5. Reach the second tab and play the muted video.

Expected Result:
The Muted video should play without any sound.

Actual Results:
The Muted Video has sound.

I also did a Mozregression on this issue and here are the results:

INFO: Last good revision: 74bb778f78793e82cfcae11446387795cb4d4180
INFO: First bad revision: a51746f37520891be96522dbce8d1bade45d8b14
INFO: Pushlog:
https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=74bb778f78793e82cfcae11446387795cb4d4180&tochange=a51746f37520891be96522dbce8d1bade45d8b14

Hmm it must be Bug 1515549, I have a couple of other issues because of that.

Fixed by backed out the offending patch - Bug 1515549

I have reproduced this bug with Nightly 66.0a1 (2019-01-11) on Linux 32bit.

Bug is fixed now on latest Beta 66.0b7

Build ID : 20190211185957
User Agent : Mozilla/5.0 (X11; Linux i686; rv:66.0) Gecko/20100101 Firefox/66.0

[bugday-20190213]

I have reproduced this bug with Nightly 66.0a1 (2019-01-11) on Windows 10 , 64 Bit !

This bug's fix is Verified with latest Beta 66.0b14 !

Build ID : - 20190307095232
User Agent : - Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:66.0) Gecko/20100101 Firefox/66.0

Hi, This issue is Verified as Fixed on Windows 10 with Firefox Beta 66.0b14 (64-bit) as well as Nightly 67.0a1 (2019-03-11). I will mark this issue accordingly.