Firstly, download the Mozilla Firefox browser from the official website.
Therefore, the choice of a proxy one should use depends on the aim of your operations with a proxy server.
There is a giant amount of proxy servers all around the Web.
How to disable proxy on mac? There you will find the Proxies menu where you should select to configure the proxy automatically.
What kind to choose is up to you.
For some of them, you will have to pay for a subscription, while some of them are free.