Update: due to the long review queue here, you can also install the latest release from the github repository: https://github.com/Xenofex/autoproxy-plus. Click 'Install latest version' there to install.
No Icon: This add-on requires Firefox 29+. From my test I can see the icon. For the users didn't see the icon, are you able to see the icon in the UI customization mode?
Automatically configure your Firefox proxy based on a set of rules, which can be defined by the user, or subscribed from a remote list.
Great for you need only certain websites to be proxied, leaving others untouched.
Example: living in China, access international sites via a proxy, while acess Chinese websites without one.