Aside: emailing from a different computer -- "Reply to:" will get to the right computer. (I decided to use pasteboard, didn't wait for a better suggestion -- I hope the images are accessible.)
Problem with viewing Youtube videos on Firefox version 68.9.0 on Jessie (but not with the same version on Buster (well, at least so far): General statement of problem: On Jessie (depending on circumstances, more below), if I move the vertical scrollbar at all, the video shrinks to a tiny bar near the upper right hand corner of the screen (see screenshots). The only way I've found to undo the problem is to reload the page (and not touch the vertical scrollbar). General statement of importance / criticality of the problem (to me): I can live with this problem (aside: somewhat at least -- I was going to transition from my daily driver Wheezy system to the Jessie system, now I'm not so sure) (oh, I do plan to continue to use kmail on Wheezy for email (with mbox for email storage) -- too many problems on Jessie and Buster). The point of saying I can live with this is that I'm probably not going to put much effort into finding and solving the problem unless someone else has some experience with the same problem. (I have googled, maybe with the wrong searchwords, but have not found anything of real relevance -- I did find some problems that mentioned scrolling but nothing like this.) The problem in more detail, with screenshots: Screenshots My file name link on pasteboard discussion ff_s31_postproblem.png https://pasteboard.co/Jea4KeN.png This shows the result of the problem -- notice the dark bar near the upper right hand corner -- the video has shrunk to that size after I've moved the vertical scroll bar even a very little bit. ff_s31_noproblem.png https://pasteboard.co/Jea2HO0.png On my other computers, when I view a youtube video (without expanding it to full screen), I see this -- note the list of other videos in the column on the right hand side. ff_s31_preproblem_b.png https://pasteboard.co/Jea9W1Up.png Most of the time when I view a youtube video on my Jessie system, it looks like either this or the next screenshot. In this screenshot, notice the absence of the list of other videos to the right of the video. If I move the vertical scrollbar, the video shrinks as described above. ff_s31_preproblem.png https://pasteboard.co/Jea5z1Y0.png Most of the time when I view a youtube video on my Jessie system, it looks like either this or the next screenshot. In this screenshot, notice the absence of the list of other videos to the right of the video. If I move the vertical scrollbar, the video shrinks as described above. Very occasionally (well, once so far), somehow (magically, I presume), when I opened a youtube video on Jessie it looked like the "noproblem" screen shot -- in that case, moving the vertical scrollbar was not a problem. Has anyone here experienced something similar? This is one set of google searchwords I used: [youtube on firefox image shrinks scroll] -- suggestions for better searchwords might be helpful.