My impression it is for 64bit browsers (like IE 64 bit). I'm not sure if there is a 64bit Firefox. If you use a 32 bit browser, you still need to install the 32 bit Java. I think on their page it ...

The Java Runtime Environment (JRE) is a software package developed by Oracle Corporation. It's designed to provide a runtime environment for applications written in Java programming language.

The Java JDK (Java Development Kit) is a software development environment that creates Java applications. It includes tools and libraries that enable developers to write, compile, and execute Java ...