uMatrix in IceCat broken

[nee]

Hello, is anyone else having the uMatrix addon's filter dialog not
render in icecat versions newer than 60?

When I click on the umatrix icon it only shows the border of the dialog
with everything transparent in the center.

I'm using uMatrix 1.4.0 from:
https://addons.mozilla.org/de/firefox/addon/umatrix/

and Icecat 68.7.0-guix0-preview1 everything works on 60.7.0-guix1
I tried some other version before and rolled back to 60.7, because it
also had the bug. Also no problems in my distro's firefox 75.
I also uninstalled and reinstalled the addons with no change seen.