Groundspeed Firefox add-on

Groundspeed, an open source Firefox add-on to support manual webapp input validation testing.

Groundspeed allows you to modify the target web application's interface by
manipulating the forms and form elements loaded in the page, in order to
remove client-side controls and limitations.

Some of the practical uses include changing hidden fields, select drop down
lists and other fields into text fields, removing size and length
limitations on input fields and modifying JavaScript event handlers to
bypass client side validation without actually removing it.

http://groundspeed.wobot.org