Blank page instead of PDF in Palemoon

[jrfnl]

Describe the bug, issue or concern

For the printable PDF, i.e. a request on the https://coronacheck.nl/nl/print/print-vaccinatie page, a blank page is displayed instead of the PDF(s) when using the PaleMoon web browser.

I checked the FAQ and could not find any information about only a limited set of browsers being supported.

To Reproduce

Steps to reproduce the behavior:

1. Install PaleMoon
2. Go to https://coronacheck.nl/print
3. Login with Digid for vaccinated or otherwise get to the state to get a valid QR Code
4. Click on either of the two "Open PDF" buttons
   
5. See a pristine blank page open in a new tab without access to the PDF (I moved the tab to a new Window for the screenshot)
   

Expected behavior

The PDF should display or be offered for download.

Desktop (please complete the following information):

• OS: Windows 10 Pro 21H1 build 19043.1288
• Browser: PaleMoon
• Version: 29.1.0 64 bit

Governance

• I've read the contributing document https://github.com/minvws/.github/blob/master/CONTRIBUTING.md
• I've read and understand the Code of Conduct https://github.com/minvws/.github/blob/master/CODE_OF_CONDUCT.md
• I understand that any contributions or suggestions I made may make it into the actual code. I've read the License https://github.com/minvws/nl-covid19-notification-app-coordination/blob/master/LICENSE.txt and the contributor license agreement https://github.com/minvws/nl-covid19-notification-app-coordination/blob/master/CLA.md

[jrfnl]

Extra info: when the tab first opens, I can (very briefly) see the controls for my default in-browser PDF viewer showing, then the page goes blank. If it would help, I can create a short video showing this.