i don't know if it is a browser issue, but on firefox the text in messages is invisible.

Same here, in Firefox ESR 140. Could be related to privacy extensions, or the dev is just using some extremely new (or non-standard) API.

it's not ublock, but it must be some other extension or setting. it works on an empty profile

Worked fine for me, even on Linux. Maybe you have some sort of blocker extension?