For users that take privacy serious, Progressive Web Apps and the Push API and Notifications API are a real headache. They offer good performance and service, but privacy wise they are not that nice. Something like a supercookie. You like them but somewhere you know, you don’t really want them.

So in Firefox, Service Worker APIs are hidden and cannot be used when the user is in private browsing mode.

But also when users have Delete cookies and site data when Firefox is closed checked, sites can not register a Service Worker.

An error in the Javascript console will show up:

Failed to register/update a ServiceWorker for scope ‘https://domain/path’: Storage access is restricted in this context due to user settings or private browsing mode.

SecurityError: The operation is insecure.

Most solutions  suggest that the user should change or uncheck that setting, but that is not necessarily needed. A better solution is to create an exception for a that particular site. Like there own. Or they want a limited set of sites they trust to enable service workers.

Press the Manage Permissions button and add an exception for your domain.

That way you can use Progressive Web Apps or service workers on a selected collection  of trusted sites, and still keep your privacy settings on a high level.

Coincidence or not since version 57 Firefox supports a headless mode. Chromium also introduced this feature at version 57.

firefox --headless --screenshot shot.png https://dev.webonomic.nl

Will run  without GUI and put a screenshot in your working directory called shot.png. If you omit to specify the a filename, the default is screenshot.png.

Since Firefox stable is now at version 56, you’ll need Firefox-developer for now to get this working.

Another nice thing is the format of the screenshot that is created. For width it will take the device-width, the resolution of your desktop, but it will render a full website, 100% height, sot it will output the layout-viewport, not just the visual viewport.

To get the visual-output you need to set the window size option:

firefox-developer --headless --window-size 360,640 --screenshot https://dev.webonomic.nl

This will create a responsive layout (mobile phone Galaxy S5 dimensions) for this website.

For the moment only the  png format seems to be supported. If you try saving to a screenshot.jpg file you’ll end up with a png file called screenshot.jpg

User-agent Firefox –headless

Mozilla/5.0 (X11; Linux x86_64; rv:57.0) Gecko/20100101 Firefox/57.0

this is actually the same User-Agent as manually running Firefox as a browser. I take that as a plus; if we want the Internet of Things (IoT), it should be a democratic Internet of Things.