Rated 5 out of 5 stars

Great theme - I've used it for ages.
For a FF18 fix Google for Silvermel and go to the developers site. Right-click on the Download button and then 'save as'.
Navigate to the downloaded silvermel_bundle_1.5.4.xpi file and change the extension to .zip
Open with WinZip or WinRar but do not extract. Double click the install.rdf file which will then open in Notepad. Edit the lines
<em:maxVersion>17.*</em:maxVersion>
and change the 17 to something like 20. Save the file and close Winzip/Winrar saying yes when prompted to update the file.
Rename the archive back to .xpi and install to Firefox.
You can now update to FF version 18.

This review is for a previous version of the add-on (1.5.4.1-signed).