Starting a temporary web server the easy way...

Open a terminal/command prompt, assuming that Python is installed, and
run the following...

    $> cd "/path/to/game/folder"
    $> python -m http.server 8000
    
    ...However, you may need to use 'python3' instead of 'python'
    ...Also, instead of 'cd', you can use the "Open terminal here"
       option that most modern operating systems have.
    
If a termprary web server has started, you will see something like the
following in the terminal...

    Serving HTTP on 0.0.0.0 port 8000 (http://0.0.0.0:8000/) ...
    
Next, open a modern web browser with JavaScript, HTML5, and WebGL
support. Go to the URL bar and type 'localhost:8000' and press ENTER.
With any luck, you will see your game start. Make sure to left-click on
the game's viewport to lock the mouse and use ESC to unlock. You may
need to enable WebGL by using 'about:config' in the web browser URL
bar.

When you are done testing, you can stop the temporary web sever by
selecting selecting terminal window and use CTRL+c.

CAUTION
=======
Starting a temporary web server this way is easy but it offers no 
security, such as passwords. Also, anyone connected to the same router
could ENTER your computer's current IP address with the port number and
also test your game. If you start a temporary web server in a directory
without an existing "index.html" file, others on the same router could
gain read-only access to those files in the directory and all
sub-directories from the location you started the temporary web service.
They may even be able to do this anyway if using something other than
a web browser. However, technically this is helpful with file-sharing
if you are not so paranoid about this sort of thing.