It's also the other way around. A lot is still done in Mozilla which don't uses Rust.
I guess the best advice I got in similar cases, is to do what you like best in your free time, which is preferably related. It's much harder to keep motivated otherwise, and there's no guaranteed way to a Mozilla job.
Lucky for me, I came across Rust before I had the thought of trying to get a job at Mozilla, and found that I enjoy programming with it a ton! I think that you're right though. I should branch out to more than just Rust and keep in mind other places that could be just as good or better than trying for just Mozilla specifically.
We're a place where coders share, stay up-to-date and grow their careers.
We strive for transparency and don't collect excess data.