What does “Blocked” really mean in the Firefox developer tools Network monitoring?

Question

The timing section of the Firefox Network Monitor documentation, \"Blocked\" is explained as:

Time spent in a queue waiting for a network connection.

Answer 1

Time spent in a queue waiting for a network connection.

The browser imposes a limit on the number of simultaneous connections that can be made to a single server. In Firefox this defaults to 6, but can be changed using the network.http.max-persistent-connections-per-server preference. If all connections are in use, the browser can't download more resources until a connection is released.

Source : https://developer.mozilla.org/en-US/docs/Tools/Network_Monitor

It's very clear that the browser fixes the limit to 6 concurrent connections per server (domains/IP), the OS question is not very relevent.