Rated 5 out of 5 stars

to use the theme with ff 3.6.8
1. download the theme
2. open the .jar (you can rename it to .zip if your archiver doesn't support .jar-files) archive and
3. open the install.rdf with notepad and
4. edit the line 8 to em:maxVersion="3.7" />
5. save
6. drag the theme file to the add on window