Firefox 4.0 beta — as well as IE and Opera — do not send name/value for input type=”image”; only .x and .y coordinates are sent.
Note, this is when clicking the input image with a mouse. When navigating using keyboard, focusing on it, and pressing enter, then the name does get submitted.
If you need to use an image button as a submit button in a form then you have to pass a hidden value to process the form.
then in test.php page
process the request