I'm seeing a strange behavior where it "stalls" intermittently. The
rendering engine seems to randomly pause activity (i.e. not responsive to
scrolling input), and these pauses can last for several seconds. It also
appears to affect video playback.
I had the same problem on my laptop with an integrated Intel graphics
card, I believe the issue started around the time of the 5.2 kernel
release.
There were a couple of threads on www.reddit.com/r/archlinux where
people reported similar bugs.
Some of the tweaks mentioned in the wiki page on Intel graphics
(https://wiki.archlinux.org/index.php/Intel_graphics#Troubleshooting)
appear to be relevant, but I was not able to fix the problem on Xorg,
and after waiting for a few kernel and firefox updates I ended up
switching browsers.
For the past month or so I've been trying Wayland out, I've been back on
firefox since then and haven't experienced any graphics issues
whatsoever.
Cheers,
Miguel