Try as I might, I could not get java to run in Firefox 3 on Ubuntu 8.04.  Turns out to be a really simple fix.

Eirik Hoem’s Blog had the answer to my problem:

I’ve been struggling with lava support for Firefox after upgrading from Ubunut 7.10 to 8.04. All I had to do was to remove the package called icedtea-gcjwebplugin. Now, I don’t know my way around java anymore, but at least it did the trick. Worth a shot if you have problems.