We previously enabled service-worker-debugging when the sw-e10s-refactor was enabled. However the latest changes from Bug 1231213 will break service worker debugging.
"[...] there is no way to get the nsIWorkerDebugger. Previously it was obtained in the parent process from a WorkerPrivate object, but now all of the WorkerPrivate objects have been moved into the child process [...] I guess Service Workers debugging is completely broken until we coordinate how to implement getting and using the nsIWorkerDebuggers"
Based on this we should review the state of service worker debugging as soon as Bug 1231213 lands and update our UI accordingly.
We can simply update https://searchfox.org/mozilla-central/source/devtools/shared/multi-e10s-helper.js in order to disable start/debug features from the new about:debugging, but we should check if other features also need to be disabled. (or if the UI is significantly broken etc...)