[CentOS] A firefox/CentOS 7 oddity

I just switched to a new workstation, running C 7, the other day.

I was looking at a blog, and in the thread of cmts, I wanted to play this
one youtube video. I listened, then closed the tab. The video that had
been *above* it in the thread started playing, and hasn't stopped. Every
other time until now that I've done this, closing the tab shuts down the
video....

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