Bug 1837467 - Enable dom.abort_script_on_child_shutdown everywhere. r=smaug

Now that we start the ShutdownKill timer only after we actually sent the shutdown message, we want to ensure that a content process that we know will die but did not yet receive the shutdown message will start to idle as early as possible in case the parent process is too busy to send the shutdown message right away.

Differential Revision: https://phabricator.services.mozilla.com/D180960

modules/libpref/init/StaticPrefList.yaml

@@ -4894,7 +4894,7 @@
 # Controls if a content script will be aborted on child process shutdown.
 - name: dom.abort_script_on_child_shutdown
   type: bool
-  value: @IS_NIGHTLY_BUILD@
+  value: true
   mirror: always
 
 - name: dom.max_chrome_script_run_time