Bug 1636423 - Enable SSE on Nightly. r=Honza

Differential Revision: https://phabricator.services.mozilla.com/D83894

browser/app/profile/firefox.js

@@ -2210,8 +2210,12 @@ pref("devtools.netmonitor.features.webSockets", true);
 // netmonitor audit
 pref("devtools.netmonitor.audits.slow", 500);
 
-// Disable the EventSource Inspector.
-pref("devtools.netmonitor.features.serverSentEvents", false);
+// Enable the EventSource Inspector in Nightly.
+#if defined(NIGHTLY_BUILD)
+  pref("devtools.netmonitor.features.serverSentEvents", true);
+#else
+  pref("devtools.netmonitor.features.serverSentEvents", false);
+#endif
 
 // Enable the Storage Inspector
 pref("devtools.storage.enabled", true);