--- ./mozilla-firefox.SlackBuild.orig	2016-11-16 12:12:10.068029005 -0600
+++ ./mozilla-firefox.SlackBuild	2016-11-16 12:41:26.774085280 -0600
@@ -220,6 +220,10 @@
 # needed for PGO.
 echo ". \$topsrcdir/browser/config/mozconfig" > .mozconfig
 
+# Build using clang:
+echo "export CC=clang" >> .mozconfig
+echo "export CXX=clang++" >> .mozconfig
+
 # Mozilla devs enforce using an objdir for building
 # https://developer.mozilla.org/en/Configuring_Build_Options#Building_with_an_objdir
 mkdir obj