PurpleBunny provides a place to add and read comments about web pages. With PurpleBunny, you can

PurpleBunny provides a Firefox toolbar that you add to your Firefox browser. You use the toolbar to read and write comments for the page you are currently reading. You can also set the toolbar to alert you when there are comments about the current page you are viewing.

The comments you add are weaved into a blog. As you write comments, you are actually blogging! Anyone who visits the comment pages within PurpleBunny can read other comments you have written for other pages.

Like blogs, PurpleBunny contribute content to the web. It turns you from being a content provider to being a content consumer. But unlike blogs, a thread of discussion is focused on a particular web page rather than a particular author.

It's a ?mozilla extension.