Firefox 3 how-to Rated 5 out of 5 stars

It seems to work OK with FF3 if you "spoof" the max version:

(1) Install 7-zip (7-zip.org) and syn (syn.sf.net)
(2) Download the Link Pad xpi installer
(3) Open the xpi with 7-zip
(4) Inside the xpi, open manifest.rdf with syn.
(5) In the Firefox section, change the max version from 2.0.0.* to 3.*
(6) Save & close. When prompted allow 7-zip to update the archive.
(7) Drop & drop the modified xpi file into Firefox to install it.