>Firefox replaces more code in a month than Rusts' entire codebase even contains.

Point taken. Rust + LLVM is almost half of Firefox though, and probably at least equivalent in terms of necessary skill. It is also not clear how much of that code could be removed without much loss of functionality.

>Rusts' expenses are massively subsidized by donated staff time from over a dozen major tech companies.

This is called having a selling point. If Firefox offered anything besides not being Chromium, people would work on it without getting paid by Mozilla.

There's no such thing as a developer tooling subsidy for a web browser.