Bug 1551273 - Turning on DS for non-nightly users (#5137)

* turn on DS for en-US and select locales for nightly

* locales check

lib/ActivityStream.jsm

@@ -225,7 +225,11 @@ const PREFS_CONFIG = new Map([
         "US": ["en-CA", "en-GB", "en-US", "en-ZA"],
         "CA": ["en-CA", "en-GB", "en-US", "en-ZA"],
       })[geo];
-      const isEnabled = IS_NIGHTLY_OR_UNBRANDED_BUILD && locales && locales.includes(locale);
+
+      // Enable for US/en-US in all channels.
+      // Enable for specific geos and locales for Nightly.
+      const isEnabled = (geo === `US` && locale === `en-US`) || (IS_NIGHTLY_OR_UNBRANDED_BUILD && locales && locales.includes(locale));
+
       return JSON.stringify({
         api_key_pref: "extensions.pocket.oAuthConsumerKey",
         collapsible: true,