Currently, there is a hard dependency on dev-lang/rust. This means a ~2-3x increase of Firefox compile time, and installing Rust likely has no other advantages even to Rust developers, since we prefer staying up-to-date with rustup. This probably requires creation of a virtual/rust package (c.f. #609438). Thanks!
If you feel I have closed your bug and it is still a current issue, please reopen and update it completely. We will not work bugs that have no ebuild in tree any longer or can not be reproduced with a current system. Thank You for your support and understanding The Mozilla Team
