Rated 4 out of 5 stars
Number one on my list. Very fast, very clean.
I'd like non-feed links to simply display the linked page rather than throwing an "invalid feed" error. And I'd like an option for all links to just display the page, not render the feed.
Of course, Sage has gone obsolete just as I discovered it. Good on Mike for picking it up and fixing it for FF 3.0. His current version is 1.9.2 (patched).
C'mon, Mozilla, update this page with Mike's version.