Needs some "pushing" ;) Rated 4 out of 5 stars

Will fail on large pages (example: http://www.quora.com/Whats-the-most-epic-photo-ever-taken) as every other extension that rely on canvas. Also on Firefox 4.0.1 / Aurora and Minefield builds (20100509).
Hope author will push report to Mozilla guys who will finally fix it.