Microsummaries is relatively new and it was a feature that snuck its way into Firefox 2.0, but not many know about it. If you need to catch up on Microsummaries, check out the Mozilla wiki on Microsummaries.
A disadvantage to creating Microsummaries is that you need a good understanding of XML and XPath. Johannes la Poutré has created an excellent Microsummaries builder for those who want to move ahead and create their own Microsummaries.
The best way to look at Microsummaries is that it provides a way to add additional titles to your page that someone bookmarks. When someone bookmarks one of your pages that contain a microsummary, they have a choice of which title they want to save the bookmark as. For those interested, I will be talking about Microsummaries in a future post.
This extension is definitely for the hard core, who ride the crest of the technology wave, but for the rest of the Firefox users, just keep in mind that Microsummaries will be an important asset in the future.