Firefox broken on second monitor

[BillCarlson]

After update to firefox 89.0+build2-0ubuntu0.18.04.2, firefox appeared completely broken. Restored history showed a bunch of blank or messed up windows (NOT pages). My system is dual monitor with one monitor in portrait mode.

As part of chasing a fix in a clean profile, got lucky and moved a window to the main, landscape monitor and lo`, it drew correctly. Moving window half on one monitor, half on second showed a working half and messed up half.

Starting Firefox in safe-mode on second monitor worked correctly. Only extension in place is uBlock Origin. See screenshot.

System is Bionic 18.04 updated 2021-06-05, after which issue noted.

Please advise if additional information is needed.

[BillCarlson (bill-carlson)]

about:config
layers.acceleration.disabled -> true
Restart browser.

Second monitor displays correctly.

[Balint Reczey (rbalint)]

I have also observed Firefox stopping refreshing windows when I added a new external monitor to a laptop screen running awesome VM. On Focal, the laptop is a Lenovo X1 Yoga 2nd gen.

[Balint Reczey (rbalint)]

Setting layers.acceleration.disabled -> true resolved the issue for me, too.