Your JRE has nothing to do with any potential JS errors on this site. We don't and never will use any Java classes for the core of the site (other than the IRC page).
Validate this by going into the Prefers and turning off Java.
As you cannot update/modify or in any way change the Javascript component in Firefox I can only assume something else is blocking the script executing properly: Firewalls can and often DO block JS scripts from executing, so look at that. Also check you have Javascript ticked and enabled in your Prefs and finally that you're not blocking any of the files our site requires.
As mentioned above, I use Firefox 0.8 exclusively on my PC and Linux box and do NOT have the Java runtimes installed because they're a waste of space to be honest. For me the code snippets expand they way they should and the post box also. The pop-up menus at the top of every page also work and are indeed faster in Firefox than in IE, which just goes to show how good the Javascript component of Firefox is. If you are on a page that doesn't work - try this: Click on the Tools menu and click on Javascript Console and see what errors and warnings you have *related to this site*.
Cheers,
Rich
With our species on the edge of extermination,
with no prospect but a horrible death,
we actually played games.