--- a/layout/tools/reftest/reftest-preferences.js
+++ b/layout/tools/reftest/reftest-preferences.js
@@ -43,8 +43,10 @@
     // Disable interruptible reflow since (1) it's normally not going to
     // happen, but (2) it might happen if we somehow end up with both
     // pending user events and clock skew.  So to avoid having to change
     // MakeProgress to deal with waiting for interruptible reflows to
     // complete for a rare edge case, we just disable interruptible
     // reflow so that that rare edge case doesn't lead to reftest
     // failures.
     branch.setBoolPref("layout.interruptible-reflow.enabled", false);
+    // Don't try to connect to the telemetry server.
+    branch.setBoolPref("toolkit.telemetry.enabled", false);

--- a/testing/profiles/prefs_general.js
+++ b/testing/profiles/prefs_general.js
@@ -183,8 +183,11 @@ user_pref("browser.cache.use_new_backend
 // Don't connect to Yahoo! for RSS feed tests.
 // en-US only uses .types.0.uri, but set all of them just to be sure.
 user_pref('browser.contentHandlers.types.0.uri', 'http://test1.example.org/rss?url=%%s')
 user_pref('browser.contentHandlers.types.1.uri', 'http://test1.example.org/rss?url=%%s')
 user_pref('browser.contentHandlers.types.2.uri', 'http://test1.example.org/rss?url=%%s')
 user_pref('browser.contentHandlers.types.3.uri', 'http://test1.example.org/rss?url=%%s')
 user_pref('browser.contentHandlers.types.4.uri', 'http://test1.example.org/rss?url=%%s')
 user_pref('browser.contentHandlers.types.5.uri', 'http://test1.example.org/rss?url=%%s')
+
+// We want to collect telemetry, but we don't want to send in the results.
+user_pref('toolkit.telemetry.server', 'https://%(server)s/telemetry-dummy/');