Rated 4 out of 5 stars
Try to download the xpi with right click, save as... Then rename xpi to .zip open install.rdf file with text editor. Search for 3.6.*, replace it by 4.0. Save it again, rename zip back to xpi. Finally open the xpi with Firefox 4.0. Tataaaa :)This review is for a previous version of the add-on (0.16).