That was done several times before, but Mozilla rejected such proposals.

Even if that means Firefox breaks every few weeks due to a new GTK release.

Even if that means Firefox never will properly support multi-monitor HiDPI on Linux (and not at all on X11).

Did they provide any reason, or those who make decisions there have some irrational bias and prefer GTK?

I can see why it can be harder to bind to Qt from Rust, but this is now a solved problem I think:

https://phabricator.kde.org/source/rust-qt-binding-generator...