Rated 5 out of 5 stars
Cool!!!!!! I searched so much add-on, from Wired-Marker to Highlighter but only Dog Ears do exactly what I want.
And this add-on is not abadoned at all, the author updated it on Homepage, get it here: http://yellow5.us/firefox/dogears/
Comfirmed by me, it even work on Firefox 10.0 Alpha 1 without any problem.