This article is relevant to those using a random port ("New IP on every request") with Unmetered Residential, Premium Residential, USA Rotating Datacenter, and Global Rotating Datacenter proxies.
If you have configured any of these proxies to use a random port in your browser, you will notice that the IP is not rotating for every request that you make in the browser. This is due to a limitation in all known browsers such as Firefox, Chrome, and Safari.
The reason your IP is not rotating is because your browser does not close the TCP connection after the initial request is completed. Instead, the browser will keep the network socket open for future requests.
This means we are unable to detect when you are making a new request because the browser is reusing the same connection socket multiple times.