Great extension, but it should come with a more complete list of user-agents built in (along with all the other variables) so that by default there is a longer list of web browsers and bots and mobile devices you can have Firefox impersonate, and also having different versions of each browser (including Firefox). Everything else about this extension is perfect, the only flaw is the rather short default list of user-agents. And it works perfectly in Firefox 8.0.
My focus until now has been on my other extension, Web Developer. I do hope to work on User Agent Switcher, but it will require essentially being rewritten from scratch so I’m not sure when I am going to have the time to work on it honestly.