User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:71.0) Gecko/20100101 Firefox/71.0

Steps to reproduce:

1. entered text into the URL bar

Actual results:

the area where completion results are shown was rendered with transparent background.

Expected results:

Since the introduction of the "hoovered" address completion / suggestion component (which I don't like a lot, by the way - where is the added benefit?), I saw a few times that the component is rendered with transparent background. If the component is hidden and re-created everything works again.

System:
Fedora Linux 30 + Mesa updates

• Intel "HD", Core 57 540m, OpenGL 2.1
• KDE + Compositition Manager turned on
• WebRender disabled (does not work because GPU too old)

Bugbug thinks this bug should belong to this component, but please revert this change in case of error.