Also make sure you have all the other proper Java programs and libs installed.
Sometimes more than one java is installed (as a system choice).. so you might want to view the: update-alternatives --config java, command, to see what is going on there.
OpenJdk is usually the best choice for me for my system java.. and I use gcj v. 0.92 in my mozilla broswers java,(ff and seamonkey).
Also make sure you have only one java plugin installed, even if it doesn't show up in your about
I'm not sure about fed, but in debian the 64 bit version of the plugin needs to be manually installed... but I'm not sure.. it's been awhile since I'v had to mess with it... either way, in debian it (libgcjwebplugin.so) gets placed in: