User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:83.0) Gecko/20100101 Firefox/83.0

Steps to reproduce:

Webrender enabled.
Firefox 83.0~b5+build1-0ubuntu0.20.04.1
Ubuntu 20.04
Sway 1.5

Actual results:

Certain add on popups appear blank when you click on them. Native popups (like the hamburger or library menus) work fine. You can see it on the screen recording with privacy badger and bitwarden add ons.

This is a regression on Firefox 83 and is also present in firefox nightly. Firefox 82 works fine.

When I disable webrender, it gets weirder. Clicking on the add on buttons doesn't display anything unless Firefox's window is not displayed full-width - you can see I'm forcing this on the second video by bringing a terminal window in and out of the workspace.

Also, sometimes, when the popups refuse to work (with webrender on) and I click on the hamburger menu, the whole UI freezes - the menu does not appear, opening new tabs with ctrl+t shows nothing on screen, however it is happening because as soon as I focus on some other window all the tabs appear suddenly. It's not like they trigger the new tab animations, one frame aren't there and the next there they are.

I've tried on a pristine profile and it happens. Not at first, but after some use.

On my normal profile it happens as soon as I install bitwarden after running "refresh firefox". I have firefox sync enabled.