I asked around and here is a response I've got.
We recently implemented CSSMarginRule support in CSSOM in 127 (behind the flag) so there is good chance we’re going to implement the CSS part, too.
Hi @rheakuh2
Can you share URL of the page that doesn't work in Firefox and some steps to reproduce the problem we could follow and see it on our machines?
I like the idea, thank you for posting!
I filed a request for enhancement in our bug tracker
https://bugzilla.mozilla.org/show_bug.cgi?id=1905877
Honza