Firefox works with VoxForge Java applet on Linux

Ubuntu & Linux Java

(see: How To Install Java on Ubuntu with Apt-Get)

install OpenJDK (Java on Ubuntu) and Icedtea (browser plugin)

$ sudo apt-get install default-jre

$ sudo apt-get install icedtea-7-plugin

restart firefox

Fedora & Linux Java

(see: Java FAQ)

install OpenJDK (Java on Fedora) and Icedtea (browser plugin)

$ su -c "dnf install java-1.?.0-openjdk"

$ su -c "dnf install icedtea-web"

restart firefox

Fedora and Oracle Java

You need to follow the instructions on this page: Use the Java plugin to view interactive content on websites, which then point you to Oracle's Manual Installation and Registration of Java Plugin for Linux article for help installing or updating Java on your Linux system.

Basically, you need to install Oracle version of Java.  Then create a link to the Java plugin file is included as part of that install in Mozill'a plugin directory, as follows:

1. go to firefox plugin directory:

$ cd ~/.mozilla/plugins

2. create link to the Java browser plugin:

for Intel-based computers:

$ ln -s /usr/java/latest/jre/lib/i386/libnpjp2.so .

or for AMD-based computers:

$ ln -s /usr/java/latest/jre/lib/amd64/libnpjp2.so .

3. restart firefox