Automatic Proxy Configuration Url, default to use no proxy if script can't be loaded

At work we are using a script to configure the proxy settings. This works fine as long as I am in the VPN or corporate network. However, when I use FF at home the script cannot be loaded (which is expected), but in order to access the internet I need to manually change the proxy settings or use a proxy switch add on. This is getting pretty annoying as I need to switch the network settings a lot. Is there a way to default the network setting to use "no proxy" if the script cannot be loaded?