--- a/browser/app/profile/firefox.js
+++ b/browser/app/profile/firefox.js
@@ -1271,17 +1271,21 @@ pref("browser.newtabpage.rows", 3);
 
 // number of columns of newtab grid
 pref("browser.newtabpage.columns", 5);
 
 // directory tiles download URL
 pref("browser.newtabpage.directory.source", "https://tiles.services.mozilla.com/v3/links/fetch/%LOCALE%/%CHANNEL%");
 
 // activates Activity Stream
+#ifdef NIGHTLY_BUILD
+pref("browser.newtabpage.activity-stream.enabled", true);
+#else
 pref("browser.newtabpage.activity-stream.enabled", false);
+#endif
 
 // Enable the DOM fullscreen API.
 pref("full-screen-api.enabled", true);
 
 // Startup Crash Tracking
 // number of startup crashes that can occur before starting into safe mode automatically
 // (this pref has no effect if more than 6 hours have passed since the last crash)
 pref("toolkit.startup.max_resumed_crashes", 3);

--- a/browser/extensions/activity-stream/moz.build
+++ b/browser/extensions/activity-stream/moz.build
@@ -11,8 +11,10 @@ FINAL_TARGET_FILES.features['activity-st
   'bootstrap.js',
 ]
 
 FINAL_TARGET_PP_FILES.features['activity-stream@mozilla.org'] += [
   'install.rdf.in'
 ]
 
 JAR_MANIFESTS += ['jar.mn']
+
+BROWSER_CHROME_MANIFESTS += ['test/functional/mochitest/browser.ini']

--- a/browser/extensions/activity-stream/test/functional/mochitest/browser.ini
+++ b/browser/extensions/activity-stream/test/functional/mochitest/browser.ini
@@ -1,12 +1,8 @@
 [DEFAULT]
-# XXX This defaults to forcing activity-stream tests to be skipped in m-c,
-# since, as of this writing, mozilla-central itself is still turned off.
-# The tests can be run locally using 'npm run mochitest' which does various
-# overrides.
-skip-if=!activity_stream
+skip-if=!nightly_build
 support-files =
   blue_page.html
 
 [browser_as_load_location.js]
 [browser_getScreenshots.js]
 skip-if=true # issue 2851