--- a/browser/config/mozconfigs/linux64/common-opt
+++ b/browser/config/mozconfigs/linux64/common-opt
@@ -1,13 +1,11 @@
 # This file is sourced by the nightly, beta, and release mozconfigs.
 
-# TODO remove once configure defaults to stylo once stylo enabled
-# on all platforms.
-ac_add_options --enable-stylo=build
+. $topsrcdir/build/mozconfig.stylo
 
 ac_add_options --enable-update-channel=${MOZ_UPDATE_CHANNEL}
 ac_add_options --with-google-api-keyfile=/builds/gapi.data
 ac_add_options --with-mozilla-api-keyfile=/builds/mozilla-desktop-geoloc-api.key
 
 . $topsrcdir/build/unix/mozconfig.linux
 
 # Needed to enable breakpad in application.ini

--- a/browser/config/mozconfigs/linux64/debug
+++ b/browser/config/mozconfigs/linux64/debug
@@ -1,14 +1,13 @@
 ac_add_options --enable-debug
 ac_add_options --enable-dmd
 ac_add_options --enable-verify-mar
 
-# TODO remove once configure defaults to stylo once stylo enabled
-ac_add_options --enable-stylo=build
+. $topsrcdir/build/mozconfig.stylo
 
 MOZ_AUTOMATION_L10N_CHECK=0
 
 . $topsrcdir/build/unix/mozconfig.linux
 
 # Needed to enable breakpad in application.ini
 export MOZILLA_OFFICIAL=1
 

--- a/browser/config/mozconfigs/linux64/debug-static-analysis-clang
+++ b/browser/config/mozconfigs/linux64/debug-static-analysis-clang
@@ -4,16 +4,17 @@ MOZ_AUTOMATION_L10N_CHECK=0
 
 . "$topsrcdir/build/mozconfig.common"
 
 ac_add_options --enable-debug
 ac_add_options --enable-dmd
 
 # Disable stylo until bug 1356926 is fixed and we have >= llvm39 on centos.
 ac_add_options --disable-stylo
+unset LLVM_CONFIG
 
 # Use Clang as specified in manifest
 export CC="$topsrcdir/clang/bin/clang"
 export CXX="$topsrcdir/clang/bin/clang++"
 
 # Add the static checker
 ac_add_options --enable-clang-plugin
 

--- a/browser/config/mozconfigs/linux64/opt-static-analysis-clang
+++ b/browser/config/mozconfigs/linux64/opt-static-analysis-clang
@@ -3,16 +3,17 @@ MOZ_AUTOMATION_PACKAGE_TESTS=0
 MOZ_AUTOMATION_L10N_CHECK=0
 
 . "$topsrcdir/build/mozconfig.common"
 
 ac_add_options --enable-dmd
 
 # Disable stylo until bug 1356926 is fixed and we have >= llvm39 on centos.
 ac_add_options --disable-stylo
+unset LLVM_CONFIG
 
 # Use Clang as specified in manifest
 CC="$topsrcdir/clang/bin/clang"
 CXX="$topsrcdir/clang/bin/clang++"
 
 # Add the static checker
 ac_add_options --enable-clang-plugin
 

--- a/browser/config/mozconfigs/linux64/valgrind
+++ b/browser/config/mozconfigs/linux64/valgrind
@@ -3,12 +3,13 @@
 ac_add_options --enable-valgrind
 ac_add_options --disable-jemalloc
 ac_add_options --disable-install-strip
 ac_add_options --disable-gtest-in-build
 
 # Rust code gives false positives that we have not entirely suppressed yet.
 # Bug 1365915 tracks fixing these.
 ac_add_options --disable-stylo
+unset LLVM_CONFIG
 
 # Include the override mozconfig again (even though the above includes it)
 # since it's supposed to override everything.
 . "$topsrcdir/build/mozconfig.common.override"

--- a/browser/config/mozconfigs/win32/common-opt
+++ b/browser/config/mozconfigs/win32/common-opt
@@ -1,13 +1,11 @@
 # This file is sourced by the nightly, beta, and release mozconfigs.
 
-# TODO remove once configure defaults to stylo once stylo enabled
-# on all platforms.
-ac_add_options --enable-stylo=build
+. "$topsrcdir/build/mozconfig.stylo"
 
 . "$topsrcdir/browser/config/mozconfigs/common"
 
 ac_add_options --enable-update-channel=${MOZ_UPDATE_CHANNEL}
 ac_add_options --enable-jemalloc
 
 if [ -f /c/builds/gapi.data ]; then
   _gapi_keyfile=c:/builds/gapi.data

--- a/browser/config/mozconfigs/win32/debug
+++ b/browser/config/mozconfigs/win32/debug
@@ -1,15 +1,13 @@
 . "$topsrcdir/build/mozconfig.win-common"
 MOZ_AUTOMATION_L10N_CHECK=0
 . "$topsrcdir/browser/config/mozconfigs/common"
 
-# TODO remove once configure defaults to stylo once stylo enabled
-# on all platforms.
-ac_add_options --enable-stylo=build
+. "$topsrcdir/build/mozconfig.stylo"
 
 ac_add_options --enable-debug
 ac_add_options --enable-dmd
 ac_add_options --enable-profiling  # needed for --enable-dmd to work on Windows
 ac_add_options --enable-verify-mar
 
 # Needed to enable breakpad in application.ini
 export MOZILLA_OFFICIAL=1

--- a/browser/config/mozconfigs/win64/common-opt
+++ b/browser/config/mozconfigs/win64/common-opt
@@ -1,13 +1,11 @@
 # This file is sourced by the nightly, beta, and release mozconfigs.
 
-# TODO remove once configure defaults to stylo once stylo enabled
-# on all platforms.
-ac_add_options --enable-stylo=build
+. "$topsrcdir/build/mozconfig.stylo"
 
 . "$topsrcdir/browser/config/mozconfigs/common"
 
 ac_add_options --enable-update-channel=${MOZ_UPDATE_CHANNEL}
 ac_add_options --enable-jemalloc
 if [ -f /c/builds/gapi.data ]; then
   _gapi_keyfile=c:/builds/gapi.data
 else

--- a/browser/config/mozconfigs/win64/debug
+++ b/browser/config/mozconfigs/win64/debug
@@ -1,18 +1,16 @@
 . "$topsrcdir/build/mozconfig.win-common"
 MOZ_AUTOMATION_L10N_CHECK=0
 . "$topsrcdir/browser/config/mozconfigs/common"
 
 ac_add_options --target=x86_64-pc-mingw32
 ac_add_options --host=x86_64-pc-mingw32
 
-# TODO remove once configure defaults to stylo once stylo enabled
-# on all platforms.
-ac_add_options --enable-stylo=build
+. "$topsrcdir/build/mozconfig.stylo"
 
 ac_add_options --enable-debug
 ac_add_options --enable-dmd
 ac_add_options --enable-profiling  # needed for --enable-dmd to work on Windows
 ac_add_options --enable-verify-mar
 
 # Needed to enable breakpad in application.ini
 export MOZILLA_OFFICIAL=1

--- a/build/macosx/mozconfig.common
+++ b/build/macosx/mozconfig.common
@@ -1,9 +1,7 @@
 if test `uname -s` = Linux; then
   . $topsrcdir/build/macosx/cross-mozconfig.common
 else
   . $topsrcdir/build/macosx/local-mozconfig.common
 fi
 
-# Enable stylo in automation builds.
-# Can be removed after bug 1375774 is resolved.
-ac_add_options --enable-stylo=build
+. $topsrcdir/build/mozconfig.stylo

--- a/build/mozconfig.common
+++ b/build/mozconfig.common
@@ -9,19 +9,16 @@
 # architectures, though note that if you want to override options set in
 # another mozconfig file, you'll need to use mozconfig.common.override instead
 # of this file.
 
 mk_add_options AUTOCLOBBER=1
 
 ac_add_options --enable-crashreporter
 
-# Tell the build system where to find llvm-config for builds on automation.
-export LLVM_CONFIG="${TOOLTOOL_DIR:-$topsrcdir}/clang/bin/llvm-config"
-
 # Enable checking that add-ons are signed by the trusted root
 MOZ_ADDON_SIGNING=${MOZ_ADDON_SIGNING-1}
 # Disable enforcing that add-ons are signed by the trusted root
 MOZ_REQUIRE_SIGNING=${MOZ_REQUIRE_SIGNING-0}
 
 ac_add_options --enable-js-shell
 
 . "$topsrcdir/build/mozconfig.automation"

--- a/build/mozconfig.no-compile
+++ b/build/mozconfig.no-compile
@@ -5,8 +5,9 @@ unset CC
 unset CXX
 unset HOST_CC
 unset HOST_CXX
 unset RUSTC
 unset CARGO
 unset MAKECAB
 unset TOOLCHAIN_PREFIX
 unset BINDGEN_CFLAGS
+unset LLVM_CONFIG

new file mode 100644
--- /dev/null
+++ b/build/mozconfig.stylo
@@ -0,0 +1,6 @@
+# Tell the build system where to find llvm-config for builds on automation.
+export LLVM_CONFIG="${TOOLTOOL_DIR:-$topsrcdir}/clang/bin/llvm-config"
+
+# TODO remove once configure defaults to stylo once stylo enabled
+# on all platforms.
+ac_add_options --enable-stylo=build