These changes will take effect with the next major release of FoxyProxy Standard, Plus, and Basic for Firefox, likely in August 2017 but definitely before Firefox 57 in November 2017. This is because WebExtensions are going to be the only supported way of developing Firefox add-ons by November 2017. And WebExtensions do not yet support the capabilities we need for our API.
This API was the only one its kind offered by any proxy add-on, for any browser. Among other things, it enabled websites to manipulate your proxy settings (with your permission). For example, with the proxy:// protocol, you could click a link on a webpage and have your Firefox proxy settings changed automatically–no tweaking on your part. This was commonly used by websites that published free proxy server lists… click a link, change your proxy server. Don’t like that one? Click another link on the webpage to change your proxy server again. But no more.
Once support for these features return to Firefox add-ons, we’ll re-implement them.