Bug 1593995 - Turn layout.css.notify-of-unvisited off for now. r=smaug

I'll figure out how to make it fast, but meanwhile this should fix the
regression.

Differential Revision: https://phabricator.services.mozilla.com/D54922

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

modules/libpref/init/StaticPrefList.yaml

@@ -4779,7 +4779,7 @@
 # Whether we get notified of history queries for visited even if unvisited.
 - name: layout.css.notify-of-unvisited
   type: RelaxedAtomicBool
-  value: @IS_NIGHTLY_BUILD@
+  value: false
   mirror: always
 
 # Whether we always restyle / repaint as a result of a visited query