* [https://developer.mozilla.org/en-US/docs/Tools/Network_Monitor Firefox Network Monitor] (built-in from version 23)
* [https://addons.mozilla.org/fr/firefox/addon/firebug/ Firebug Add-on]
* [https://addons.mozilla.org/en-US/firefox/addon/modify-headers/ ModifyHeaders Add-on] gives a way to modify the '''HTTP headers''' you are sending to a Web site. It will not work for JavasScript scripts looking for navigator.userAgent.
===== Others =====
* [http://httpie.org/ httpie] (CLI)
* [http://www.opera.com/dragonfly/ Opera Dragonfly] (Presto)
=== Client Side User Agent Detection ===