Bug 1624321 - Enable DOM node arena allocation r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D68060

--HG--
extra : moz-landing-system : lando

modules/libpref/init/StaticPrefList.yaml

@@ -2461,7 +2461,7 @@
 
 - name: dom.arena_allocator.enabled
   type: bool
-  value: false
+  value: true
   mirror: once
 
 - name: dom.serviceWorkers.enabled