How can I change the user agent in Firefox to switch to IE7?

So, at work they have blocked access to the internet with Firefox and now I have to use the awesome Internet Explorer 7 for all of my browsing. I know how to change the value of “general.useragent.extra.firefox” through about:config, but when I try to change it to IE, I still can’t access any website.

I have Firefox 3.5.6 and Internet Explorer 7 installed on my desktop. Now, would I have to use the user agent that IE7 is currently using on my computer or can I use any IE user agent? The user agent that IE7 is using right now is: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 1.1.4322; .NET CLR 2.0.50727; InfoPath.2; .NET CLR 3.0.04506.30; .NET CLR 3.0.04506.648; .NET CLR 3.5.21022). Do I just copy that and use it as the user agent in Firefox?

How can I make this work???