Bremsstrahlung

Customizing Safari and the web.

Safari 5 introduces Safari Extensions, a new way for developers to enhance and customize the browsing experience. Create buttons for the toolbar or make your own extension bar. Change the way web content appears. Add controls to web pages. Safari Extensions are built with web standards, so you can do it all using the power of HTML5, CSS3, and JavaScript.

Finally!

To elaborate: This was always the one area where I thought Safari lagged behind the other (good enough to use) browsers, and nobody at Apple seemed to care. Things like PithHelmet (whose effective loss I still mourn, although I now, out of pragmatism, use GlimmerBlocker) and GreaseKit were forced to exist as unsupported hacks which could, and frequently did, break for no very good reason¹.

This bit, however, looks like it bears watching:

Signed and sandboxed.

Every Safari extension is signed with an Apple-provided digital certificate — free with the Safari Developer Program. The certificate protects the extensions you develop from tampering and ensures that updates come only from you. Safari Extensions also include built-in defenses like sandboxing, which safeguards your extensions from being used to access information on a user’s system.

On the one hand, it sounds like this is a carefully thought out approach which will, among other things, prevent shenanigans like what went on between Adblock Plus and NoScript for Firefox. On the other hand, it looks like it will squeeze out honest tinkering even with things which wouldn't mind being tinkered with.