Say what? OK, this is a little advanced but it's kind of cool so I'm posting it. :-)

The user agent is the fancy name for your browser. The reason that it is important is that it tells the web server what kind of browser you're using. Some sites actually will serve different files based on what your user agent is. For example, you Mac users (like me), have you ever been to a software site that offered you the Mac version to download without you having to tell it that you're on a Mac? That's because they detected your user agent.

The search engine bots also use user agents. Here's a list:

Google: Googlebot (Something like this: Googlebot/2.1 (+http://www.googlebot.com/bot.html))
Yahoo: Yahoo! Slurp (like this: Mozilla/5.0 (compatible; Yahoo! Slurp; http://help.yahoo.com/help/us/ysearch/slurp))
MSN: MSNBOT (like this: msnbot/1.0 (+http://search.msn.com/msnbot.htm))

You can get a complete list here.

Did you ever wonder if your site (or your competitor's site) is showing something different to the search engines than it shows to regular folks? Many do. It's a Black Hat (baaaaad) technique called Cloaking. (And before you think about doing it, it's a very quick way to get banned from the engines.) But, if you find one of your competitors doing it you should report them. That's just keeping the playing field level. Here's how to change your user agent in Firefox so you can become a sleuth:

1. First, enter "about:" (sans quotes) as the URL in Firefox (no http or anything else). You'll see some groovy information about your browser.
2. In Firefox, enter "about:config" as the URL.
3. Right click to get the contextual menu and select New>String.
4. As the preference name enter "general.useragent.override".
5. As the value, enter "Googlebot" or whatever you want.

Now, enter about: again and see what you see. You should see Googlebot (or what you entered) as the Build Identifier. Pretty cool, huh? Now, go find those baddies.

Oh, and don't forget to change it back when you're done. To do that, just go back to about:config and right click on general.useragent.override and select "Reset".