Firefox lags scrubbing / skipping on video platforms

Hi!
I have been using firefox since I installed Manjaro and I’ve intermittently had this problem. I can’t quite tell what is the source of it, if updating the system or anything else.
The problem is that when I skip / scrub videos on vimeo, youtube or other platforms with my left / right keys, the video takes something around 1-2 seconds to restart playing. It’s a very annoying problem which does not happen in Chromium.
I tried uninstalling firefox with pacman, also removing the .mozilla folder in my home folder, in the .cache folder, and reinstalling and the issue does not disappear. I also tried the aforementioned steps and disabling hardware acceleration in ff, enabling webgl.disable in about:config, and nothing seems to solve it.

I also tried a fresh install of Manjaro Cinnamon in a VM and the problem does not happen, which makes me believe the problem might be around the gpu configuration or, in someway, between firefox and the GPU.

Finally, when scrubbing, I see CPU usage spike, which does not happen in Chrome.

When I open firefox from the terminal, no output appears when scrubbing, and the only thing that shows when starting is the following warning:

[Parent 4831, Main Thread] WARNING: Failed to call GetIdletime(): GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.gnome.Mutter.IdleMonitor was not provided by any .service files
: 'glib warning', file /build/firefox/src/firefox-120.0/toolkit/xre/nsSigHandlers.cpp:187

** (firefox:4831): WARNING **: 18:27:18.944: Failed to call GetIdletime(): GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.gnome.Mutter.IdleMonitor was not provided by any .service files

+info:
running up-to-date Manjaro Cinnamon on a E5-1630 v3 with 16GB of RAM and an NVME drive, with a RTX 3060. No other app running while testing.

Thank you a lot!

Hi. I happen to have a similar behavior here, but it does not happen all the time.

I never investigated much because the frequency of this is low, maybe 10 times a day max.

hardware:
AMD Ryzen 5 3600 6-Core Processor
Video: AMD Navi 23 Radeon RX 6600/6600 XT/6600M
Audio: (on-board) Starship/Matisse HD Audio Controller
RAM: 32 GiB 2133 MHz; SWAP: 2.0 GiB
/ is mounted on a cryptsetup+lvm volume on a SSD

It happens more frequently after a restart but stops happening after a good amount of use. It’s hard to detect the trigger.

Theres a number of possiblities. Topmost might be hardware acceleration (or lack thereof).

But thats all documented.

So, for an out of left field suggestion…

about:config

dom.ipc.processCount.file = 2

The default is 1 … try increasing to 2 or more.

Oh. And checking the performance of safe-mode might be instructive.

firefox --safe-mode