Download the source…

by brute force
If you don't know GIT and Github, and you don't want to know, and you just want to download the source,
  1. Navigate to this site;
  2. On the page, find a button entitled either Download ZIP, or simply ZIP;
  3. Press on it: this will download the zipped source code.
- or -
elegant, and smart
You want to follow fixes and extensions, you know git, or you don't care installing it
⇒ clone the repository!
  1. Open a terminal and enter:
    git clone https://github.com/Jaxo/fxosstub.git
  2. use git pull for keeping up with the latest revision
- or -
the nice, social, collaborative way
You have a GitHub account, so I won't insult you at explaining what  git fork  means.
Your Pull Requests will be welcome.