> Isn't that on the other direction, with Firefox using new features which are only available on the latest stable version of Rust, meaning it "breaks" on old v

> Isn't that on the other direction, with Firefox using new features which are only available on the latest stable version of Rust, meaning it "breaks" on old versions of Rust? No. In openSUSE, we've been blocked for far too long because the latest Firefox releases did not compile with the latest Rust releases. Some enterprising individual went and debugged it and patched Firefox to work with newer Rust and we were finally able to land it, but it took months and we missed out on 1.37, 1.38, and almost 1.39. This happens because openSUSE's build service rebuilds everything dependent on Rust at build-time automatically, and if things fail to build, new Rust can't land in the distro. This is not the first time it has happened, and I suspect it won't be the last. So, I meant what I said.