Firefox 89, page scrollbar is invisible

Does anybody else have this issue?

I have a netbook and a desktop, both fully updated, both with XFCE and almost all settings identical.

After updating Firefox from 88 to 89, the page scrollbar is like 100% transparent on the majority of the sites (not on this site, though). I can see neither the scrollbar itself nor the scroll “thumb” (the element that you can drag to navigate). However, if I put my mouse pointer in the area where the scrollbar should be and click or hold the left mouse button, I can drag the invisible thumb and navigate. So actually, the scrollbar is there, it is just invisible.

And it is not exactly Firefox issue, because:

a. it is observed even with a clean Firefox profile on my desktop;

b. but on my netbook it is not observed, even on the old Firefox profile.

I’m putting this topic in Browsers section because still, it is observed only in Firefox. However, it is likely that the issue is partially connected with some other settings. It is not GTK theme, however, because I tried switching the theme, to no avail.

Maybe someone has any ideas where I can look for the source of the problem? Like, is there a way to export all XFCE settings to a single text file, so the settings from the netbook and the desktop can be compared?

Try with a different system theme.

Hi! Yes, I have tried different GTK themes, but the issue persists.

You can make the scroll bar visible again by changing the theme with Settings / Appearance. I have solved the problem like this.

I have this issue only when using materia-gtk-theme (I use the dark ones only).