Mashup Guide

I know about the Firefox add-on/extension mechanism but what about the corresponding element of other web browsers? Here's what a series of quick web searches turned up:

Firefox

• Firefox Extension Development Tutorial :: Overview
• XULPlanet.com

Opera

• Opera widgets: Opera Widgets – Weather, News, and More
• Opera User Javascript — Opera's take on Greasemonkey: UserJS.org – User JavaScript for Opera

Internet Explorer

• CodeGuru: Internet Explorer Extension
• an official forum
  • Welcome – MSDN Forums
  • Internet Explorer Developer Center
  • IE Development

Safari

• Pimp My Safari: about:
  It was started as a reaction to the sites cataloguing Firefox extensions. Many excellent plugins for Safari have been developed, but because Safari doesn’t have an official ‘extension architecture’, many don’t know of these extensions.

I'll see how much 'll be able to cover these various mechanisms in detail in the book.