YouTube playback is low-fps (choppy, laggy) in R4.2 in Firefox starting from Fedora-40 templates

balko · October 28, 2025, 12:26pm

YouTube playback is low-fps (choppy, laggy) in R4.2 in Firefox starting from Fedora-40 templates.

I remember, that fullscreen playback in R4.1 was way better, much smoother. So, I tried old official templates but with the same Firefox profile, on the same 1080@60fps video, and found out an important thing:

If I use fedora-39 official template, the playback in Firefox 119 in fullscreen is smooth, almost flawless.
If I use fedora-40 or later official templates, the playback in Firefox 132 in fullscreen for the same video is not good, it plays like 15 FPS.

Note 1: If I make the Firefox window rather small, like 30% of the screen, the playback is smooth in both cases, with fedora-39 and fedora-40 templates.

Note 2: I have no frame drops, it’s not a CPU issue per ser, it’s regression in fedora-40 template or in Firefox that is provided their.

Note 3: I have cinema/theater mode off on YouTube, otherwise Qubes OS lags a lot more.

Any ideas, how should I restore smooth playback in Firefox? I think finding the workaround would help many people, who probably thinks that it’s Qubes OS to blame for the problem.

balko · October 28, 2025, 5:01pm

Update with a workaround:

I installed flatpak version of Firefox and checked that YouTube playback on fedora-42 in flatpak version of Firefox is smooth (like it was on fedora-39).

If I open the same video on the same hardware but in native fedora firefox it is playing much worse (low-fps playback).

Qubes OS should address the issue, because it affects probably all users who plays YouTube or other media in Firefox.

balko · October 29, 2025, 3:37am

Reportered as an issue here:

github.com/QubesOS/qubes-issues

YouTube and other video playback in Firefox got major regression in fedora-40/41/42 templates (low fps, micro-lags)

opened 03:36AM - 29 Oct 25 UTC

jamke

P: default

### Qubes OS release R4.2. ### Brief summary YouTube and other video playback i…n Firefox got major regression in fedora-40/41/42 templates: the video gets micro-lags, it looks like the video output in fullscreen becomes like 10 fps instead of 30-60. Changing template from fedora-39-* to fedora-40-* or later brings this problem. I tried `fedora-39` (official template) and YouTube playback in Firefox (v119) in full-screen was smooth and flawless. When template is changed to `fedora-40-xfce` (also official template) playback in Firefox (v132) in the same qube, the same firefox user profile in full-screen the playback is LOW fps, like 10 frames per second or something instead of 30-60. The same happens with fedora-42. So, I can confirm, that regression happened between fedora-39 and fedora-40, between R4.1 and R4.1 Qubes OS. ### Steps to reproduce * Install fedora-39 and fedora-42 templates. * Create 2 qubes with those templates accordingly. * Play fullscreen YouTube video in both qubes in Firefox. I used 1080@60 video on 1440p display. ### Expected behavior Video playback is without lags in both qubes. ### Actual behavior Video playback is kind of laggy in `fedora-42` one, with micro-lags brinnging framerate to like 10 fps instead of 30-60. `fedora-39` has way smoother playback on the same hardware and everything else. ### Workaround Using flatpak Firefox instead of default one in Qubes OS workarounds the issue. I installed flatpak version of Firefox and checked that YouTube playback on fedora-42 in flatpak version of Firefox is smooth (like it was on fedora-39). In the same qube when I open the same video on the same hardware but in native fedora firefox it is much worse (low-fps playback). ### Additional information * I suspect codecs/libs problem. But I do not know how to force firefox in fedora-42 template to use the same "good" codecs as flatpak version does. I mean I installed RPMFusion and media sections from it, including ffmpeg instead of ffmpeg-free, but it did not improve playback in native firefox. * 99% of Qubes OS users are probably affected by this issue, and think that lags (low frame rate) of playback is a problem of Qubes OS or weak CPU, but in fact it isn't.

Atrate · October 29, 2025, 8:29am

Another workaround it to use picture-in-picture mode, this seems to speed up youtube by quite a lot for me.

balko · October 29, 2025, 8:54am

Can you confirm, that installing flatpak version of Firefox also improves playback for you?

You can install without modification of template.

Create new qube, set fedora-42-xfce template (or any other),
In this qube install and run like that with --user flag:

flatpak --user remote-add --if-not-exists flathub https://dl.flathub.org/repo/flathub.flatpakrepo

flatpak --user install org.mozilla.firefox

flatpak --user run org.mozilla.firefox

Try YouTube playback of some 1080@60fps (or higher) video fullscreen .

Atrate · October 29, 2025, 9:16am

I can confirm that this works and reduces lags significantly.

balko · October 29, 2025, 2:27pm

Great. So, the question is how to fix it for 99,99% of other Qubes OS users who do not know and kind of suffer from terrible browser video playback starting from R4.2.