Suppress telemetry banner.

test/resources/firefox/user.js

@@ -34,3 +34,5 @@ user_pref("dom.w3c_touch_events.enabled", true);
 user_pref("extensions.checkCompatibility", false);
 user_pref("extensions.installDistroAddons", false); // prevent testpilot etc
 user_pref("browser.safebrowsing.enable", false); // prevent traffic to google servers
+user_pref("toolkit.telemetry.prompted", true); // prevent telemetry banner
+user_pref("toolkit.telemetry.enabled", false);