Bending the Browser. An entirely new form of web programming.
That’s revolutionary. No need to build scrapers, or interface with APIs if they even exist yet. Or build proxies. Or send feedback. The Web is bendable today. Programmers and hopefully utlimately users, can directly modify and extend the Web transparently.
One idea to solve some design problems: rewrite rss links to point at the user’s favorite aggreagator.
It is possible to generally modify CSS in Mozilla, like this project on skinning gmail. Still a few steps away from ease of use. I imagine a XUL app, which parses a sites HTML and CSS, and presents that in an editor for user modification.