this post was submitted on 06 Dec 2025
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Low FPS in Firefox on one monitor (lemmy.world)
submitted 2 weeks ago by chaospatterns@lemmy.world to c/linux@programming.dev
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I switched to Kubuntu 25.10 on my desktop from Windows 10 and every since, I've noticed that Linux on my primary monitor has felt very choppy with a low FPS. Animations are choppy and slow. As soon as I drag it to my second monitor, everything is faster and has higher FPS. This doesn't happen on Windows. testufo.com shows ~20fps on the problematic monitor I also haven't noticed this behavior with any other programs. There are spikes to 50fps and smoother animations when I open the Firefox menu, but then it goes back to 20fps. Chromium on the same monitor is faster and shows 50+fps. Games on this monitor also are higher fps

The primary monitor is configured to 60Hz, the second monitor is 143.97Hz. I've got an Nvidia GeForce 2070 with the NVIDIA driver (open kernel) metapackage from nvidia-driver-580-open installed, 32GB of RAM, plenty of CPU, and no other programs or tabs open even.

What could cause this issue and how can I fix it?

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[–] Redjard@lemmy.dbzer0.com 6 points 2 weeks ago (1 children)

I recall this happening on my higher refreshrate and resolution screen on X11 and nvidia (iirc a 2070 super). Moving to wayland fixed it.
I mainly noticed frame drops in videos in forefox, but I'm sure scrolling was also affected.

It probably manifests on a per usecase basis since it depends on how exactly the gpu or x11 is loaded. Whatever it is, it's some consequence of x11 being flawed at its core abd just not scaling well with modern usecases.

In my case I was forced onto wayland after I got my new better monitor due to how choppy x11 felt.
I had 2 1080p 60Hz and got a 4k 120/144Hz screen.

[–] chaospatterns@lemmy.world 1 points 1 week ago* (last edited 1 week ago) (1 children)

Interesting. I played around with X11 vs Wayland settings just to see what different configurations give me

  • MOZ_ENABLE_WAYLAND=1 /snap/bin/firefox - Exhibits low FPS issue
  • MOZ_ENABLE_WAYLAND=0 DISABLE_WAYLAND=1 /snap/bin/firefox - Actually feels fast like it should be. Most animations feel faster, some are still choppy though. It's hard to tell.

It seems like running with X11 sort of the problem? Which seems unexpected and concerns me since I know distros are starting to default to Wayland.

[–] Redjard@lemmy.dbzer0.com 1 points 1 week ago

That would make it a different problem than what I saw. Either your compositor has bugs not present in its xwayland, or firefox has bugs in its wayland implementation that don't occur under x11. Seeing this is snap, that could also be causing the issue.

concerns me since I know distros are starting to default to Wayland

xwayland will be supported for a long time to come, so this would only affect users that don't know about this "fix" yet. You should be able to use firefox in x11 mode until this is fixed.

It would be good if you could check if this happens with a native (non-snap) firefox installation running on wayland. Ideally also if you could try it in a different dwm, probably kde since you are presumably using ubuntu with gnome.

[–] dgdft@lemmy.world 5 points 2 weeks ago

Check if you have hardware acceleration enabled for Firefox. It’s usually disabled OOTB for some reason.

https://support.mozilla.org/en-US/kb/performance-settings

[–] frongt@lemmy.zip 4 points 2 weeks ago (1 children)

The slow monitor is plugged into the graphics card, not the motherboard, right?

[–] chaospatterns@lemmy.world 1 points 1 week ago (1 children)

Yep, both are plugged into the graphics card. Other programs and games are a lot faster.

[–] frongt@lemmy.zip 1 points 1 week ago

Does anything change if you change refresh rates or display scaling? Or change between X11 and Wayland?

[–] Tai@mander.xyz 2 points 2 weeks ago (1 children)

I had the exact issue. My monitors were different resolutions, so I scaled my 4k display so it matched my 1440p monitor which was like a 175% increase. Linux doesn't seem to like fractional scaling, and it worked normally when scaling was set to 200%.

YouTube videos were still choppy though. Turns out the ambient mode on videos was causing that

[–] imecth@fedia.io 2 points 1 week ago

Fractional scaling is a compositor issue, not a linux issue, so in this case kwin. But yes, fractional scaling in general is always problematic as there's no way to cleanly multiply pixels by fractions, so you get wonky fonts, UI that doesn't quite fit... and whatever hacks your compositor has on top to make it look better, it's best to avoid it if possible and only increase the font size.

[–] chaospatterns@lemmy.world 1 points 1 week ago

Just an update. Firefox 146 just dropped with:

  • Firefox now natively supports fractional scaled displays on Linux (Wayland), making rendering more effective.

After upgrading to 146 and natively using Wayland, it feels faster. Some fade animations are still choppier, but on average it's at least tolerable.

Thanks for the suggestions everyone.

[–] just_another_person@lemmy.world 0 points 1 week ago

Disable Hardware Acceleration