diff -up thunderbird-68.11.0/config/makefiles/rust.mk.no-rust-lto thunderbird-68.11.0/config/makefiles/rust.mk

--- thunderbird-68.11.0/config/makefiles/rust.mk.no-rust-lto	2020-08-04 12:01:08.172071480 +0200

+++ thunderbird-68.11.0/config/makefiles/rust.mk	2020-08-04 12:26:25.927808414 +0200

@@ -50,8 +50,8 @@ ifndef MOZ_DEBUG_RUST

 # Pass -Clto for older versions of rust, and CARGO_PROFILE_RELEASE_LTO=true

 # for newer ones that support it. Combining the latter with -Clto works, so

 # set both everywhere.

-cargo_rustc_flags += -C lto

-export CARGO_PROFILE_RELEASE_LTO=true

+#cargo_rustc_flags += -C lto

+#export CARGO_PROFILE_RELEASE_LTO=true

 endif

 endif