Update: I’m an idiot. This is a feature that’s part of Lifehacker’s Better GReader Firefox extension that I installed the other day. I just now noticed the behavior, and though it was part of Google Reader itself. Still, a cool feature – check out Better GReader for that and more! And sorry for the false alarm. Here I thought I was breaking news on a new feature! 😉
When I clicked the post title, instead of opening in a new tab, as usual, it opened an inline preview of the entire target web page, right there inside Google Reader.
There’s a new “Preview” button at the bottom of the entry, too, where you can toggle the preview on and off.
Haven’t read anything from Google about this feature yet, but it’s neato! 🙂