Good morning/evening/night guys,
since I installed the latest Tumbleweed updates yesterday (many many packages were upgraded, including Firefox), fullscreen videos played in Firefox have got low fps and constantly lag. This happens at least on Youtube and Vimeo. No problems when playing videos inside the webpage (no fullscreen mode). This happens even when viewing in very low resolution (360p and higher resolutions). 240p is as smooth as it should be, even in fullscreen. This doesn’t happen in Chrome.
I’m using Wayland, haven’t tried with Xorg yet. I’ll try and keep you updated.
What can I do to grab more data on the problem?
Thanks 
I see the same problem for a longer time also on Xorg.
Have you tried to ssh into the machine from another one, to see more details?
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Hendrik
Hello!
This happens on Xorg as well, I can confirm. However, I must repeat that I’ve only started experiencing this problem a couple of days ago.
Another thing worth noting is that sometimes, 480p playback is smooth in fullscreen, but only when the Youtube player starts playing the video at that quality from the beginning. As soon as I try to increase it to 720p or 1080p, all resolution from 360p to 1080p start lagging, and the 240p becomes the only smooth resolution. The lags and stutters involve only the images of the video, the audio track is played correctly.
I’ve captured some top outputs during fullscreen playback. Firefox uses around 100% of the cpu, which seems normal to me (it uses 70-80% of the CPU during non-fullscreen playback). The load average was around 1.5 and I’m on a dual core laptop with Intel Hyperthreading (4 threads), so I’d say there’s no weird cpu usage, it’s just Firefox that started behaving badly all of a sudden.
News: Ok, I’ve found a workaround that allows me to live with the problem: changing playback resolution on YT *before *switching to fullscreen mode is enough. Playback will be smooth as expected. I wonder if it’s a Firefox bug or if it’s a YT bug that arises only when using Firefox. If someone can tell me whom I can inform about the problem, it’d be great. I’d be glad to help to fix it.
Second edit: the above post is not correct. That workaround works only sometimes.
My (weird) workaround:
- start the Plasma-Full-Wayland session
- use FF in Xorg compatibility mode (“GDK_BACKEND=x11 firefox”)
This strange combination works for me …
Then I’m afraid the root cause of our problems is different. Your workaround doesn’t work for me. I’ll try to report this issue to the openSUSE Firefox devs/mantainers.