Java and JavaScript are completly different languages. However, Netscape Navigator (I don't know about mozilla) has fairly good bridging.

Also, it may be possible to perlify Mozilla's JavaScript engine. (Which is designed to be used as a library seperate from mozilla, IIRC.) That would certianly be a worthwhile, and probably rather difficult, project.

Update: I actualy did Recall Correctly. The javascript interpreter mozilla uses is called JSRef, AKA SpiderMonkey. There is also Rhino, which is pure Java, and thus probably harder for you to use.

Update: Fixed links.