Grey vs white visual bug (Firefox)

[svandragt]

Heya I'm not sure if the correct background colour of posts is very light grey or white but I'm seeing both:

home:

single:

Latest firefox.
Linux: openSUSE Tumbleweed 20230102

It looks fine on Chrome based browsers.

[kadamwhite]

Interesting! It is meant to be white. @svandragt can you determine which rule is causing the not-white background in Firefox?