The “Scribe” extension in Firefox allows to save form entries before form submission (File/Save Entry) and then reload it again later on on the same page (File/Open entry). You can have multiple data sets for the same Web page.
This has great value on e-commerce projects, where tedious form information has to be reentered often.
https://addons.mozilla.org/extensions/moreinfo.php?id=102 (Get Firefox first)