Yes. You mutate when trying to manually install extensions(a theme is an extension)
Here it goes....
Ready?
.....
goto c:\Document And Settings\username\Application Data\Mozilla\Firefox\Profiles\deault.e3f\extensions
create a directory with the name being the guid for the theme as it should show in the install.rdf.
Put a folder called chrome inside that directory
Put the .jar in the chrome directory.
Go back to the extensions directory and edit Extensions.rdf and add this
Code:
</RDF:Description>
<RDF:Description RDF:about="urn:mozilla:theme:{29852C08-1E91-4889-A6BF-C77F91D6A8F3}"
em:version="0.10"
em:name="Littlefox"
em:description="Littlefox 1.0, designed for optimal screen usage, leaving lots of room
for browsing"
em:creator="Alfred Kayser"
em:homepageURL="http://www.geocities.com/alfredkayser/mozilla/themes.htm"
em:internalName="littlefox/1.0">
<em:targetApplication RDF:resource="rdf:#$JZXda3"/>
</RDF:Description>
editing it to use the info from the install.rdf file.