why do XPI's have jars

JohnSmith <[email protected]>
Newsgroups gmane.comp.mozilla.devel.xpinstall
Organization SBC http://yahoo.sbc.com
Message-ID <[email protected]>
As I understand it, JARs are java archives.  However, I have yet to see 
any XPI JARS have any java in them.  Shouldn't they really be zips?
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