How to change the User Agent in Firefox

Can any one tell me How to Changing User Agent form Firefox Web Browser ? i heard that when we changing user agent, we can get access some of the restricted part of a website. That has extra contents that normally open only to bots, or search engine crawlers.

Thanks for your reply .

You can use User Agent Switcher add-on extension for Firefox.

Change the User Agent , Enter about:config in the address bar of Fire Fox.

Press the right mouse button ,,Now you will get a context menu and select "String" from the menu entry.

Now put the preference name"general.useragent.override". After that enter the new User Agent value you want Mozilla Firefox to use.

To switch the user agent immediately

In Firefox type "about: config" into the address bar and filter for "general.useragent.extra.firefox". By double-clicking, you specify what Firefox should now send. An empty field means that it sends nothing. Another option is the Firefox addon User Agent Switcher. About Tools, User Agent Switcher "quick turn around and add on" options, user agents' own pairs added. The default is IE7, Opera 4.8 and Netscape 9:25 to choose from, all with Windows Vista. Many pages adapt to the requesting browser. If they get no or false values from the user agent, set the page may not be optimal dar. If you have problems turn most comfortable with a Firefox addon back. IE8 surfers take back to Privoxy.