I assume you're referring to Rust? Who has a financial interest in Rust? I have trouble imagining Mozilla making money off of Rust directly; I don't think there's any Rust developers who wouldn't immediately jump to a fork if Mozilla put ads in Rust's documentation or decided rustc needed a default search engine.

As far as making money off of their own software written in Rust, that advantage is actually stronger if they convince everyone else Rust is stupid and not worth their time.