Browser HTML filters?

When writing filters for the Firefox Add-On 'Adblock Plus' you can write rules to completely remove certain HTML elements from the page, but filtering criteria is in fact limited to a handful of things, like class and id names and attribute values.

What I was hoping for is say a Firefox Add-On which would pass the HTML for a page to some开发者_开发技巧 arbitrary process you specify, where this process could reconstitute the HTML for the entire page in any arbitrary way and then have the browser display that. Is there a Firefox add-on that allows this or is this sort of operation commonly accomplished by some entirely different but well-known means (and perhaps not browser-specific).

Wouldn't this allow you to augment pages coming from some website to your browser with arbitrary new features, maybe from an entirely different website.

You are looking for Greasemonkey.