--- a/browser/config/mozconfigs/macosx64/beta
+++ b/browser/config/mozconfigs/macosx64/beta
@@ -2,9 +2,11 @@ if [ -n "$ENABLE_RELEASE_PROMOTION" ]; t
   MOZ_AUTOMATION_UPDATE_PACKAGING=1
 fi
 
 . "$topsrcdir/browser/config/mozconfigs/macosx64/common-opt"
 
 ac_add_options --enable-official-branding
 ac_add_options --enable-verify-mar
 
+ac_add_options --enable-lto
+
 . "$topsrcdir/build/mozconfig.common.override"

--- a/browser/config/mozconfigs/macosx64/nightly
+++ b/browser/config/mozconfigs/macosx64/nightly
@@ -4,11 +4,13 @@ ac_add_options --disable-install-strip
 ac_add_options --enable-verify-mar
 ac_add_options --enable-instruments
 
 # Cross-compiled builds fail when dtrace is enabled
 if test `uname -s` != Linux; then
   ac_add_options --enable-dtrace
 fi
 
+ac_add_options --enable-lto
+
 ac_add_options --with-branding=browser/branding/nightly
 
 . "$topsrcdir/build/mozconfig.common.override"

--- a/browser/config/mozconfigs/macosx64/release
+++ b/browser/config/mozconfigs/macosx64/release
@@ -5,13 +5,15 @@ if [ -n "$ENABLE_RELEASE_PROMOTION" ]; t
   MOZ_AUTOMATION_UPDATE_PACKAGING=1
 fi
 
 . "$topsrcdir/browser/config/mozconfigs/macosx64/common-opt"
 
 ac_add_options --enable-official-branding
 ac_add_options --enable-verify-mar
 
+ac_add_options --enable-lto
+
 # safeguard against someone forgetting to re-set EARLY_BETA_OR_EARLIER in
 # defines.sh during the beta cycle
 export BUILDING_RELEASE=1
 
 . "$topsrcdir/build/mozconfig.common.override"