Mozilla binds Firefox's fate to the Rust language

After version 53, Firefox will require Rust to compile successfully, due to the presence of Firefox components built with the language. But this decision may restrict the number of platforms that Firefox can be ported to—for now.

"The advantage of using Rust is too great,” according to maintainer Ted Mielczarek. “We normally don’t go out of our way to make life harder for people maintaining Firefox ports, but in this case we can’t let lesser-used platforms restrict us from using Rust in Firefox,” he wrote.