Different access to the internet

Hello
I want to use Firefox in two different connections to the internet.
1 - At home I connect directly to the internet.
2 - At work I have a proxy server.
My problem is that when I get to work I need to manually change the network settings to manual proxy configuration, and when I get home I need to change to direct connect to internet.
Is there anyway to configure this automatically?? I try auto-detect and automatically and didn't work...

Thanks

Jaime