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

I have a server that takes several seconds to respond, which allowed me to cross-reference the firefox measurement with a wireshark trace. I see that the first SYN is sent out immediately. The end of the "Blocked" time corresponds to when the Server Hello comes back.

I couldn't relate the end of "TLS setup" to any wireshark packet. It extends a few seconds belong the last data that is exchanged on the initial TLS connection.

Bottom line: it doesn't look like the time spent in "Blocked" and "TLS setup" is very reliable, at least in some cases.

My setup has a TLS reverse proxy that forwards the connection with SNI. I'm not sure if that might be related.