I'm not sure whether this question belongs on StackOverflow or SuperUser, but here goes nothing...

I'm trying to test out some basic security problems on my personal ASP.NET website to see exactly how the custom validators, etc. work when tampering with the data. I've been looking at the Firefox extension TamperData which seems to do the trick, but it doesn't feel very professional at all.

The issues I'm having with TamperData is that the textbox for the POST data is way too small to hold the ASP.NET view-state, so I have to copy that data into Emacs and then back again to be productive at all. I also don't like that there doesn't seem to be an option to only tamper with data which is from/to localhost.

Any ideas on better extensions for the task or better methods to test it?