The Microsummaries feature I proposed a few months ago in this blog--and have been developing since then--has landed in time to make Firefox 2.0 alpha2. Or rather, an initial version of it has landed. UI and other elements are still undergoing refinement.
But there's something to play with now, so play, and let me know what you think! To use the feature, you first have to install some microsummary generators, which are the things that extract microsummaries from their pages. Get started with this page of sample generators.
To install a generator from that page, just click its link (f.e. the Yahoo! Finance Stock Quote link), click OK when Firefox asks you if you want to add the generator, go to a page to which the generator applies (f.e. the Yahoo! Finance Stock Quote for Apple Computer), and then select Bookmark This Page... from the Bookmarks menu.
In the Add Bookmark dialog, select the microsummary from the Summary drop-down menu, then select the Bookmarks Toolbar from the Create in drop-down menu. Press the Add button to add the bookmark. A bookmark to the page should appear on your bookmarks toolbar (or its "chevron" overflow menu, if you're out of space on the toolbar proper) with the microsummary you selected as its label.
If you're having trouble, see this set of unit tests, which take you through step-by-step instructions for testing the feature. If you want to create your own microsummary generators, see this tutorial on the subject.
Up next: bug fixes, UI brainstorming, a presentation Wednesday at XTech, and perhaps a pre-alpha microsummary builder extension if I can get to it.