Rated 5 out of 5 stars

per James el jul. 23, 2009 · enllaç permanent

Made to work with 3.5.1 without any problems (method as oobidoobbanoobi describes in the comments below)

For those that don't know:
1: Download [don't install] and change the extension from xpi to zip
2: Modify install.rdf so that: 3.5.* - 2a: Rezip if you unzipped to make the change
3: Change the extension back to xpi
4: Drag and drop your modified xpi to a Firefox window... And install... Restart... Done