Starting with Firefox
75 , for security reasons, dedicated and shared worker scripts served with a wrong MIME type will be blocked from loading with
SharedWorker() respectively. The change has already been made to the Nightly and early Beta channels since Firefox 70, and only one compatibility issue has been reported so far.
The same change has already been made in Firefox 67 to scripts loaded with
importScripts(). Make sure your script files are always served with
Update: The novel coronavirus (COVID-19) outbreak is forcing people to spend more time online at home. Due to concerns around making the change with Firefox 75 during such an uncertain time, it has been postponed to a future release. The enforcement remains enabled on the early Beta and Nightly channels. We’ll update this note when the situation has changed.
Update 2: This change is shipping with Firefox 81.