How to use firewall:

1. Install mitmproxy

   1.1. Install prerequisites as described here:

    http://mitmproxy.org/doc/install.html  
   
    For example for debian-based systems:
    $ sudo apt-get install build-essential python-dev libffi-dev libssl-dev libxml2-dev libxslt1-dev
   

   1.2. Install mitmproxy with python package manager:

    $ pip install mitmproxy  
   

2. Edit file 'whitelist.txt'. It contains list of domains
   Note: That file must no contain any spaces before or after domain names.

3. Edit file 'access_denied_template.html'. It's name is self described. '$URL' is placeholder for domain name.

4. Configure your web client's (e.g. your browser) proxy settings to firewall's bind address: 127.0.0.1:8080

5. Run firewall from command line:

   $ ./firewall.py

6. Test it!