Bug 1506367 - Tests fail for network attempt to snippets.cdn.mozilla.net on Nightly builds r=r1cky

Differential Revision: https://phabricator.services.mozilla.com/D11561

--HG--
extra : moz-landing-system : lando

testing/profiles/common/user.js

@@ -3,7 +3,8 @@
 user_pref("app.update.disabledForTesting", true);
 user_pref("browser.chrome.guess_favicon", false);
 user_pref("browser.dom.window.dump.enabled", true);
-// Use an empty list of sites to avoid fetching
+// Use a python-eval-able empty JSON array even though asrouter expects plain object
+user_pref("browser.newtabpage.activity-stream.asrouter.providers.snippets", "[]");
 user_pref("browser.newtabpage.activity-stream.feeds.section.topstories", false);
 user_pref("browser.newtabpage.activity-stream.feeds.snippets", false);
 user_pref("browser.newtabpage.activity-stream.tippyTop.service.endpoint", "");