--- ./mozilla/config/rules.mk.orig	2020-06-06 14:59:53.000000000 -0500
+++ ./mozilla/config/rules.mk	2020-07-24 13:16:53.707149335 -0500
@@ -874,7 +874,9 @@
 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