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

In my case both waiting for network connection and DNS lookup times were pretty high, up to 2 seconds each, caused significant page load times if the page was loaded for the first time. Firefox was freshly installed without addons and just started with no other opened tabs. I tried on both Ubuntu 18.04 LTS and Ubuntu 19.04 with the same results. Although my ISP doesn't provide support, my router assignes IPv6 addresses. As it turned out the problem was the IPv6 broken network, which forced Firefox to fall back to IPv4 (of course after some time(time-out)). After I turned off the IPv6 support in Linux the requests speeded up significantly. Here is a relavant discussion: https://bugzilla.mozilla.org/show_bug.cgi?id=1452028