Oh, I see. I only vaguely remembered some changeset regarding it. I must have been mistaken, then, and it's still in use.

In any case, sneakily using nightly features can make using a different Rust version problematic, since these features are free of any stability guarantees.

Arch Linux carries a rather large patch updating some vendored dependency in order to make Firefox 78 compile with a newer Rust. https://github.com/archlinux/svntogit-packages/tree/packages...