--- a/mailnews/test/performance/common/mailnewsTestPrefs.js
+++ b/mailnews/test/performance/common/mailnewsTestPrefs.js
@@ -28,8 +28,9 @@ user_pref("mail.server.server2.name", "t
 user_pref("mail.server.server2.type", "pop3");
 user_pref("mail.server.server2.userName", "tinderbox");
 user_pref("mail.smtp.defaultserver", "smtp1");
 user_pref("mail.smtpserver.smtp1.hostname", "tinderbox");
 user_pref("mail.smtpserver.smtp1.username", "tinderbox");
 user_pref("mail.smtpservers", "smtp1");
 user_pref("mail.startup.enabledMailCheckOnce", true);
 user_pref("mailnews.start_page_override.mstone", "1.9pre");
+user_pref("mail.shell.checkDefaultClient", false);