I am able to tamper post request parameter with Tamper Data in firefox i.e when i make post request and i get the popup in firefox to change POST request parameters but in case of GET request, i get the popup but there is no way to change the request parameter.
So question is Can't we change the request parameter thru Tamper Data/Fiddler?(Yes i agree we can change it from browser address bar but that will be applicable once first request has been firect but i want to tamper some data in the very first Get Request. So i want to change GET request paramater with Tamer Data/Fiddler.Is it possible?)
You can't do that using Tamper-Data. You could use a more advanced standalone-tool, like Web Scarab (Archived page by Wayback Machine / Source Code at SourceForge) which will let you intercept and edit all portions of your web-requests.
Using fiddler, in conjunction with FiddlerScript is also an alternative.