Bug 1144693 - Disable libnotify usage on Linux until a fix is found, r=rkent

mailnews/mailnews.js

@@ -635,7 +635,7 @@ pref("mail.biff.show_balloon", false);
 #elifdef XP_MACOSX
 pref("mail.biff.animate_dock_icon", false);
 #elifdef XP_UNIX
-pref("mail.biff.use_system_alert", true);
+pref("mail.biff.use_system_alert", false);
 #endif
 
 // add jitter to biff interval