Enabling Java in Firefox
First, Click the Menu button and choose Add-Ons.
Next, on Plugins from the list of items on the left. You should see Java listed on the right.
If it is not listed, you will need to install Java. You can install Java by clicking on this link https://java.com/en/download/index.jsp
Unblocking Java in Firefox
If you have trouble opening a video, you may see this:
If you click on it, it will give you the following window. Go ahead and Allow the plugin.