I receive the error message "Your browser must have Java enabled to use the Client for Java." when attempting to load a webpage. Java has been added to firefox and the appropriate checks have been made under preferences.
Follow the instructions from: http://linux.digitalsp.com/2009/07/install-java-plugin-for-firefox-ubunt...
Let me know if this worked for you.
Another option would be to try to use the Opera browser. Opera works differently from Firefox, Firefox needs the sun-java-plugin package but Opera uses the sun-java-jre package.