I was getting intermittent freezes in firefox with KDE, X11, nvidia GPU and encountered this bug:
Bugzilla:
libx11:
Temporary Solution: Downgrading to libx11 1.8.1-3 solves this issue.
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It reproducibly happens since couple of Firefox versions ago to me (KDE / X11 / Nvidia), easiest way to trigger freeze reliably at least for my case:
- Open some video in “Picture in Picture mode” or just 2nd Firefox window
- Just type something in text-fields or use Ctrl + C / Ctrl + V to copy/paste something
It will freeze 
pretty soon.
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My Firefox doesn’t do this on KDE with libx11 1.8.2-2 
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I’ve had some weird tab issues, which I thought was javascript hanging or dying on various sites, or a updated extension regression (of which Vimium C looked suspicious due to updates)
There are two hacked libx11 packages in AUR right now that might help for those that are severely affected.
Hi, do you have a nvidia card ?
No on Kde I have an AMD card. But i do have an Nvidia on another system with Xfce. Don’t have any issues.
I have the issue on both KDE and XFCE, mostly when playing video in firefox and copy/pasting stuff…
I did a fresh install and the issue was still there. Thanks for the fix @ainz !
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@ricklinux I’ve had freezes during video playback, copy-pasting and opening new tabs. I’m on gtx1060 btw.
@Tozman Glad the fix helped.
Quite a few are having similar issue:
I don’t have this issue on my GTX 1060 installed with Xfce nor my KDE with Ryzen and AMD.
Edit:
[ricklinux@eos-kde ~]$ pacman -Qi libx11
Name : libx11
Version : 1.8.2-2
Guess you got lucky. 
Maybe or it’s the hardware?
Maybe . I’m also on ryzen with nvidia gpu on x11. Happens with firefox nightly too.
Downgraded libx11 and waiting for a fix.
Both those links don’t work.
Edit: Anyway doesn’t matter. If it’s a software issue it’s just strange why it doesn’t happen to everyone.
fixed it.