diff --git a/comm/mail/config/mozconfigs/common b/comm/mail/config/mozconfigs/common
--- a/comm/mail/config/mozconfigs/common
+++ b/comm/mail/config/mozconfigs/common
@@ -1,6 +1,3 @@
 ac_add_options --enable-application=comm/mail
 
-# Disable enforcing that add-ons are signed by the trusted root.
-MOZ_REQUIRE_SIGNING=
-
 . "$topsrcdir/build/mozconfig.common.override"
diff --git a/comm/mail/moz.configure b/comm/mail/moz.configure
--- a/comm/mail/moz.configure
+++ b/comm/mail/moz.configure
@@ -12,6 +12,7 @@
 imply_option("MOZ_CRASHREPORTER_URL", "https://crash-reports.thunderbird.net/")
 
 imply_option("--enable-default-browser-agent", False)
+imply_option("MOZ_REQUIRE_SIGNING", False)
 
 
 @depends(target_is_windows, target_is_linux)