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