Bug 1738358 - Pref on layout.css.page-size.enabled r=dholbert

Differential Revision: https://phabricator.services.mozilla.com/D129873

modules/libpref/init/StaticPrefList.yaml

@@ -7158,7 +7158,7 @@
 # Enables support for the size property inside of CSS @page rules.
 - name: layout.css.page-size.enabled
   type: RelaxedAtomicBool
-  value: @IS_NIGHTLY_BUILD@
+  value: true
   mirror: always
   rust: true