Firefox usually creates a numbered temp file before renaming this file to the actual file to ensure that there isn't a problem with creating a new file. If Firefox isn't able to remove the actual file and rename the temp file then you are left with various numbered temp file like in your case with the serviceworker.txt file.

This can happen if security software keeps a handle on this file, so check that and make sure your security software leaves the Firefox profile folder alone. You can see by the dates of the numbered files when this happened.

Is serviceworker.txt the only file that has numbered temp files present in the profile folder ?

Those were the only numbered series (that appeared to be) temp files, all empty zero-byte files. So, if Mozilla has no program capable of laying out these "service-worker" files, they must be generated from something outside? Besides Windows itself, ZoneAlarm, and Malwarebytes are the only things I can think of...

Russ

You should only have the serviceworker.txt file and not numbered serviceworker-##.txt files.

Are the timestamps of the numbered files recent or is this going on for longer ?

You can remove those numbered files and also serviceworker.txt if its file date is not recent.

I've deleted them (all) but was able to go into my backup files and see the dates, which ranged from 2015 up thru a few days ago. I did find a few blurbs on the 'net about this being controllable thru about:Config, so I went there and toggled a few things to false. Will see how it behaves. Sorry to see Mozilla becoming more and more complex and secretive (like Google & MS) after each iteration of update. Sure miss the simple older versions!

Russ

If you can't pinpoint another application (security software) as the culprit of these numbered files then you will have to keep an eye on your profile folder and cleanup files yourself.