diff --git a/modules/libpref/init/StaticPrefList.h b/modules/libpref/init/StaticPrefList.h
index dc7d0f1ee36b..c4a3c58092b0 100644
--- a/modules/libpref/init/StaticPrefList.h
+++ b/modules/libpref/init/StaticPrefList.h
@@ -149,7 +149,7 @@ VARCACHE_PREF(
 VARCACHE_PREF(
   "layout.css.parsing.parallel",
    layout_css_parsing_parallel,
-  bool, false
+  bool, true
 )
 
 // Is support for the font-display @font-face descriptor enabled?