[azakai]

I can tell you as a former Firefox developer that that was not the case. Yes, Firefox has some dependencies copied into the tree, but deciding to do it, and the process afterwards (including updating), were very careful and slow.

Of course there may have been exceptions I am not aware of, and developers are humans that can make mistakes, but that is the overall culture I experienced. It is fundamentally different to the JS/Rust/etc. ecosystem models.