Switchproxy

Here's a link to an interesting extension tool that lets you switch between proxy configurations on your Firefox browser easily. It creates a little drop down for you to select the proxy you want to use.

It's useful if you're on a laptop and constantly on different networks. An added bonus is has a built in anonymizer for those who have a need to surf the web without divulging their identity.

As always a tool like this can be mis-used, so if you're a network administrator and want to make sure your end-users aren't mis-using something like this, you probably don't want an explicit proxy deployment in your network (see other posts on proxy deployments).