I believe that would mean reading and processing FireFox's configuration files.
There's a prefs.js file in C:\Documents and Settings\CURRENT_USER\Application Data\Mozilla\Firefox\Profiles\CURRENT_PROFILE\.
Code:
//if this line is not present, proxys are off, if the value is 1,
//then it's user-specified proxies, if 2, then automatic detection
user_pref("network.proxy.type", 1);
//if this line is present and with the value true, then FireFox uses the same proxy for all protocols
user_pref("network.proxy.share_proxy_settings", true);
//the proxys and ports (only present if they are set)
user_pref("network.proxy.ftp", "ftp.example.com");
user_pref("network.proxy.ftp_port", 21);
user_pref("network.proxy.gopher", "gopher.example.com");
user_pref("network.proxy.gopher_port", 150);
user_pref("network.proxy.http", "www.example.com");
user_pref("network.proxy.http_port", 80);
user_pref("network.proxy.socks", "whatever.com");
user_pref("network.proxy.socks_port", 999);
user_pref("network.proxy.ssl", "ssl.com");
user_pref("network.proxy.ssl_port", 132);
//specifies the socks version of proxies (only present if value is 4)
user_pref("network.proxy.socks_version", 4);