--- ./config/makefiles/rust.mk.orig	2020-07-24 12:54:18.411119017 -0500
+++ ./config/makefiles/rust.mk	2020-07-24 12:55:50.335121073 -0500
@@ -47,7 +47,9 @@
 ifndef DEVELOPER_OPTIONS
 ifndef MOZ_DEBUG_RUST
 # Enable link-time optimization for release builds.
+# Pass -Clto and CARGO_PROFILE_RELEASE_LTO=true.
 cargo_rustc_flags += -C lto
+export CARGO_PROFILE_RELEASE_LTO=true
 endif
 endif