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