YouTube Default view used to show the video on the left, with the Up Next thumbnails in a column on the right. (If a playlist was selected, it would appear at the head of the right-hand column with the Up Next thumbnails below it.) Comments appeared below the video. On three other browsers (Chrome, Opera and Vivaldi) YouTube Default view remains the same as before, but ON FIREFOX it's changed to something quite different. In the new Default view the video stretches horizontally all the way across the screen. The height is increased proportionately, and on my laptop that means that the video won't fit on the screen heightwise -- what a nuisance, I have to scroll to see the upper and lower parts of the video image: I can't see the whole thing a once. The contents of the (old view) right-hand column now appear below the video, and Comments appear below that. To get to Comments I have to scroll, scroll, scroll. It is an ungainly and confusing layout. Peculiarly, the new Default view layout is practically the same as the Theater mode. Th only difference I see is that in the new Default view the panel above the video has a white background, whereas the in the Theater mode that panel has a black background. Now there's a useful feature! I never had any use for YouTube Theater mode. I would use either the (old, user-friendly) Default view or Full Screen. Why duplicate Theater mode features and then replace Default view with them? I assume that this is a Firefox problem because the old Default view still appears on other browsers. I want it back on FIREFOX! How do I do it? BTW I meant to attach screenshots comparing the two views, but the upload didn't seem to be working.