A while ago, I said (while discussing browser extensions for Internet Explorer):
There’s extensive information about how to go about coding these yourself. The only thing that’s missing seems to be a real drive to produce these things. The only ones I’ve seen have tended to be produced by big companies, e.g. MSN, Google, Yahoo and eBay have all produced downloadable toolbars. If only Microsoft had put effort into encouraging the creation of new extensions. But it’s against their mindset – I think extensions will always be a predominantly open source thing. That’s where people are positively encouraged to add code to the browser.
But it turns out I was wrong. There’s loads of extensions for IE7, and it hasn’t even been released yet.