Are you concerned about your privacy? Or, are you blocked from some websites by a firewall? And, are you arming yourself with a proxy? In that case, AutoProxy is designed for you! A tool to help you use your proxy automatically & efficiently.
Here is a little more information about AutoProxy from the developers:
With AutoProxy, you no longer need to switch your proxy status between on & off manually. If you prefer to visit a website via proxy, just add it’s domain to AutoProxy’s preference. After that, when you surfing, specified websites will be transferred through proxy while leaving others connect directly.
You can subscribe to rule lists maintained by people who have similar requirements as you. So, you don’t need to add all proxy rules by yourself. Want this add-on? You can pick up AutoProxy from the Firefox Add-ons website.