During an initial visit to slashdot.org Firefox hangs for approx 45 seconds while the status bar says "looked up a.fsdn.com." Subsequent visits during the same browser s… (emoñe’ẽve)
This is with Preferences -> General -> Network Settings -> Enable DNS over HTTPS -> Cloudfare or NextDNS. With Firefox DoH disabled the problem is not present. [Interesting side, the machine's systemwide DNS settings are configured for Cloudfare 126.96.36.199 ]
AFAIK all other sites load normally. I've been using the Firefox DOH for several months with only the above site as a problem.
Environment: Firefox desktop 106.x and 107.x macOS 10.13.6 The problem is present in "Troubleshoot Mode" when Firefox DOH is enabled.