Comment by ftrobro

Rust was created at Mozilla and currently 11.7% of the Firefox source code is in Rust:

https://4e6.github.io/firefox-lang-stats/

That's down from 12.49% at the peak in July 2020 so I assume the conversion work was halted after the layoffs in 2020:

https://docs.google.com/spreadsheets/d/1flUGg6Ut4bjtyWdyH_9e...