Since I never remember how to do this, I figured I'd put it up here. This assumes you already have Java installed, and note this is for 32-bit. I'll be getting a shiny new 64-bit laptop very soon, and from what I understand things are a bit different on 64-bit.
- In Firefox, go to Edit -> Preferences -> Content and check "Enable Java"
- Quit Firefox
- In a terminal, cd to /path/to/firefox/plugins. On my machine and for my current version of Firefox, this is in /usr/lib/firefox-3.0.14/plugins If in doubt, locate plugins | grep firefox should narrow it down.
- Create a symlink to the Java plugin. Your path to Java may differ, but on my machine I did:
ln -s /usr/share/java/jdk1.6.0_14/jre/plugin/i386/ns7/libjavaplugin_oji.so libjavaplugin_oji.so
- Restart Firefox