Firefox Add-On, change settings based on connection

I would like to create my own Add-On that will change the settings depending on the proxy (if a proxy is used or not), is this possible? I asked in Firefox Add-On IRC but didn't answer, all users were idle.

Example:

// If proxy is enabled
lockPref("general.appname.override", "Netscape");
lockPref("general.appversion.override", "5.0 (Windows)");
lockPref("general.buildID.override", "20100101");
lockPref("general.oscpu.override", "Windows NT 6.1; Win32");
lockPref("general.platform.override", "Win32");
lockPref("general.productsub.override", "20100101");
lockPref("general.useragent.locale", "en-US");
lockPref("general.useragent.override", "Mozilla/5.0 (Windows NT 6.1; rv:31.0) Gecko/20100101 Firefox/31.0");