fishingmaniac,
If a re-boot doesn't solve this, here are a few thoughts that may help.
Firefox 3.6+ will not work correctly with any less than Java version 6 update 10.
I seem to remember having a similar problem when I upgraded my browser to FF 3.6.
Now, what I suggest you do is manually remove any trace of Java from your computer, via Add/Remove Programs (or whatever your operating system calls this application, in the Control Panel).
When you update or upgrade Java, the installer that comes with the newer version will not by default remove the older version(s).
From there, I suggest you download and install the latest version of Java, which you can find
on this page. One other thing, make sure that you have Java enabled in Firefox, you can check this by clicking on Tools > Add-Ons, the Add-Ons window will open, click on the Java listings, if the "button" to the right of the listing says Enable, it means that Java is disabled, click this to enable Java.
If this doesn't solve the problem, let me know.