How to show the active service workers in the firefox dev tools?
On about:serviceworkers (checked on Firefox 72) there is another interface from where you can also unregister or remove service workers.
Not sure why there are two different interfaces to deal with service workers in Firefox. ð
JUNE 2020 EDIT: I've noticed that on Firefox 76 from about:debugging#/runtime/this-firefox you can also now unregister service workers, functionality that previously wasn't available from this page. The funny thing is that this updated page is also on Firefox 72! The code for this page must be updated remotely without the need of updating Firefox. Didn't know that Mozilla integrated this functionality into the browser.
Type about:debugging#workers in your address bar,
or in a more natural way:
Menu -> Web Developer -> Service Workers.