diff --git a/build/unix/mozconfig.gtk b/build/unix/mozconfig.gtk
index f1451c43462..0414ba859a0 100644
--- a/build/unix/mozconfig.gtk
+++ b/build/unix/mozconfig.gtk
@@ -1,30 +1,29 @@
+# To do try builds with Gtk+2, uncomment the following line, and remove
+# everything after that.
+#ac_add_options --enable-default-toolkit=cairo-gtk2
+
 TOOLTOOL_DIR=${TOOLTOOL_DIR:-$topsrcdir}
 
-# $TOOLTOOL_DIR/gtk3 comes from tooltool, when the tooltool manifest contains it.
-if [ -d "$TOOLTOOL_DIR/gtk3" ]; then
-  if [ -z "$PKG_CONFIG_LIBDIR" ]; then
-    echo PKG_CONFIG_LIBDIR must be set >&2
-    exit 1
-  fi
-  export PKG_CONFIG_SYSROOT_DIR="$TOOLTOOL_DIR/gtk3"
-  export PKG_CONFIG_PATH="$TOOLTOOL_DIR/gtk3/usr/local/lib/pkgconfig"
-  PKG_CONFIG="$TOOLTOOL_DIR/gtk3/usr/local/bin/pkg-config"
-  export PATH="$TOOLTOOL_DIR/gtk3/usr/local/bin:${PATH}"
-  # Ensure cairo, gdk-pixbuf, etc. are not taken from the system installed packages.
-  LDFLAGS="-L$TOOLTOOL_DIR/gtk3/usr/local/lib ${LDFLAGS}"
-  ac_add_options --enable-default-toolkit=cairo-gtk3
-
-  # Set things up to use Gtk+3 from the tooltool package
-  mk_add_options "export FONTCONFIG_PATH=$TOOLTOOL_DIR/gtk3/usr/local/etc/fonts"
-  mk_add_options "export PANGO_SYSCONFDIR=$TOOLTOOL_DIR/gtk3/usr/local/etc"
-  mk_add_options "export PANGO_LIBDIR=$TOOLTOOL_DIR/gtk3/usr/local/lib"
-  mk_add_options "export GDK_PIXBUF_MODULE_FILE=$TOOLTOOL_DIR/gtk3/usr/local/lib/gdk-pixbuf-2.0/2.10.0/loaders.cache"
-  mk_add_options "export GDK_PIXBUF_MODULEDIR=$TOOLTOOL_DIR/gtk3/usr/local/lib/gdk-pixbuf-2.0/2.10.0/loaders"
-  mk_add_options "export LD_LIBRARY_PATH=$TOOLTOOL_DIR/gtk3/usr/local/lib"
-
-  # Until a tooltool with bug 1188571 landed is available everywhere
-  $TOOLTOOL_DIR/gtk3/setup.sh
-else
-  PKG_CONFIG=pkg-config
-  ac_add_options --enable-default-toolkit=cairo-gtk2
+# $TOOLTOOL_DIR/gtk3 comes from tooltool, and must be included in the tooltool manifest.
+if [ -z "$PKG_CONFIG_LIBDIR" ]; then
+  echo PKG_CONFIG_LIBDIR must be set >&2
+  exit 1
 fi
+export PKG_CONFIG_SYSROOT_DIR="$TOOLTOOL_DIR/gtk3"
+export PKG_CONFIG_PATH="$TOOLTOOL_DIR/gtk3/usr/local/lib/pkgconfig"
+PKG_CONFIG="$TOOLTOOL_DIR/gtk3/usr/local/bin/pkg-config"
+export PATH="$TOOLTOOL_DIR/gtk3/usr/local/bin:${PATH}"
+# Ensure cairo, gdk-pixbuf, etc. are not taken from the system installed packages.
+LDFLAGS="-L$TOOLTOOL_DIR/gtk3/usr/local/lib ${LDFLAGS}"
+ac_add_options --enable-default-toolkit=cairo-gtk3
+
+# Set things up to use Gtk+3 from the tooltool package
+mk_add_options "export FONTCONFIG_PATH=$TOOLTOOL_DIR/gtk3/usr/local/etc/fonts"
+mk_add_options "export PANGO_SYSCONFDIR=$TOOLTOOL_DIR/gtk3/usr/local/etc"
+mk_add_options "export PANGO_LIBDIR=$TOOLTOOL_DIR/gtk3/usr/local/lib"
+mk_add_options "export GDK_PIXBUF_MODULE_FILE=$TOOLTOOL_DIR/gtk3/usr/local/lib/gdk-pixbuf-2.0/2.10.0/loaders.cache"
+mk_add_options "export GDK_PIXBUF_MODULEDIR=$TOOLTOOL_DIR/gtk3/usr/local/lib/gdk-pixbuf-2.0/2.10.0/loaders"
+mk_add_options "export LD_LIBRARY_PATH=$TOOLTOOL_DIR/gtk3/usr/local/lib"
+
+# Until a tooltool with bug 1188571 landed is available everywhere
+$TOOLTOOL_DIR/gtk3/setup.sh