Bug 1654357 - Disable speculative omt JS parsing r=smaug

Disable speculative js parsing temporarily until a race condition in bug 1652126  is resolved.

Differential Revision: https://phabricator.services.mozilla.com/D84412

modules/libpref/init/StaticPrefList.yaml

@@ -2522,7 +2522,7 @@
 # soon as they are fetched.
 - name: dom.script_loader.external_scripts.speculative_omt_parse.enabled
   type: bool
-  value: @IS_NIGHTLY_BUILD@
+  value: false
   mirror: always
 
 # Speculatively compile non parser inserted scripts