Well, there is Kaffe.... It's a Java VM for Amiga. most of core Java is there, but AWT is pretty sketchy, according to the readme's and such. I haven't tried it, but I don't think it would work too well. Especially not for something like an entire browser in Java.
Besides, Java is "write once, TEST everywhere, anyhow"......
Hmm.... Wonder what would happen if you tried to load jazilla as a java app inside Sun Java Plug-in for Mozilla. You could have the first Mozilla running mozilla! :-P