Env-based FF browser color per Andrei de Oliveira Mosman

This extension changes the color of the browser's panel based on the host name.

Localhost: set to light green
- Development environment. Host names starting with `dev-`, or listed in the Development hostnames field, in the plugin settings. Color: another green
- QA environment. Host names starting with `qa-`, or listed in the QA host names field in the plugin settings. Color: blue.
- Production environment. Host names listed in the production host names field in the plugin settings. Color: red.

I wrote this for developers and QA personnel. The goal is to minimize mistakes when working in multiple environments.