Having gotten sufficiently annoyed at the need to maintain two Mozilla Firebird profiles just because I use a proxy in school and none at home, I decided to look up the “Automatically detect proxy configuration” option. After some digging around, this is the answer I found:

This goes into my /etc/laptop-net/profiles/school/files.d/var/www/proxy.js:

function FindProxyForURL(url,host)
{ if(isPlainHostName(host)||
    isInNet(host,"10.0.0.0","255.0.0.0")) return "DIRECT";
      else return "PROXY proxy.admu.edu.ph:3128; DIRECT";
}

and this goes into my /etc/laptop-net/profiles/home/files.d/var/www/proxy.js:

function FindProxyForURL(url,host)
{
  return "DIRECT";
}

I deleted the other profile and changed my settings to automatically detect the proxy configuration from file:///var/www/proxy.js . Tada! No more worries. It just works.