Sorry folks, this is really confusing for me and it kind of snuck up on me like fading breaks on a car. "This" computer is my main one and I use it the most. I load youtube and get the usual list of suggestions. If I moved my mouse over any, they would start to play and I would "preview" them on that screen. I could select if I wanted the audio and subtitles. All was good. Fire fox has updated and the O/S has also over time and "recently" the "preview" stopped. (Oh well. Such is life.) I didn't think much of it. Then the other day I was on ANOTHER machine (different O/S, similar/same plugins) and loaded youtube just for the sake of it and as I moved the mouse over the clips: I got the "preview". I've shared the data from this machine. Kind of difficult to do it in/on THIS post from the OTHER machine also. For clarity: It used to work. I didn't change any settings in any of the plugins/addons or FF settings. They were "working" as I wanted and so there was no reason to change them. I am guessing this is a "easy thing to fix" but the specifics of what I need to do is beyond me at this point. I'd appreciate some guidance in how t find the difference between the two machine's settings so I can get the preview to work again. Just to put it out there too: I have a "squillion" tabs open. They all seem to work and unless I really get carried away with things, Firefox 95% of the time behaves itself. Now and then it "locks up" and stops responding. The best solution is a total reboot and restart.