Change my browsers POST method data

Is there any way to access My Own Browsers (IE8, FF3.6) Session data or POST Method data? For example when an item is sending using POST method i can change it.

www.example.com/index.php?menuitem=2

change to

www.example.com/index.php?menuitem=开发者_如何转开发3

Is there any script or software to help?

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A firefox extension called HTTP Request String Editor enables you to edit the data sent to the server.

Note that you cannot change the session data itself, as it's stored on the server.

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My suggestion would be to use Fiddler. It will work across all browsers and will let you modify just about anything in the header.