Again after upgrading from Ubuntu 9.10 to 10.4, I had some issues getting Java to work with Firefox, after checking the software center, I found that the Java plugin for firefox is not working properly which broke my vpn connection.
To get this fixed, I simply followed the steps :
1- Backup your repositories files.
sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup
2- Open your repositories file:
sudo gedit /etc/apt/sources.list
3- Add the following line then close the sources.list file
deb http://archive.canonical.com/ubuntu maverick partner
4- Uninstall both icedtea6-plugin and openjdk-6-jre.
sudo apt-get remove icedtea6-plugin openjdk-6-jre
5- Install sun-java6-plugin
sudo apt-get update sudo apt-get install sun-java6-plugin sudo update-alternatives --install /usr/lib/mozilla/plugins/mozilla-javaplugin.so mozilla-javaplugin.so /usr/lib/jvm/java-6-sun/jre/lib/i386/libnpjp2.so 1
6- Close your firefox and reopen it again, it should be working smoothly.