As of today devtools codebase is involved in many BHR (Background Hang reports). For example, at least 5% of all BHR longer than 2s are related to network monitor. And devtools/client/netmonitor/src/middleware/batching.js:89 represents 80% of all BHR related to detools. You can see and track the evolution on this page: http://arewesmoothyet.com/?category=all&durationSpec=2048_65536&historical=true&payloadID=c6201da94dcb48ad9a25bfc31e22cddc&search=devtools&thread=1

It looks like BHR hangs >= 1s related to devtools drastically reduced since Nov 22th: https://arewesmoothyet.com/?mode=explore&durationSpec=2048_65536&historical=false Most likely thanks to bug 1404917 and bug 1408182. Looking at past 9 days view for hangs >=4s, the stacks also drastically changed: https://arewesmoothyet.com/?mode=explore&durationSpec=2048_65536&historical=false Before 22th, netmonitor's batching.js:89 was 83% and console's new-console-output-wrapper.js:298 was 13% of overall 4s+ hangs related to devtools. After 22th, netmonitor is 39% while console is 30%. (new-console-output-wrapper.js has two offending lines: 305 and 299). So today, netmonitor is competing with console regarding very long hangs. I hope that netmonitor is going to continue dropping down as we fix bug 1404913. On the console side, may be bug 1368100 (remove immutable) would fix long hangs as it fixed them for netmonitor?