Downloaded PDF files using Firefox on Mac are corrupted

If you look into my account, you'll see there's one admission.

I want to sign it digitally (after the user has submitted to us) and tick a few hidden fields, generate a NEW PDF with our additions and download as a PDF. But, when I try to download it, I get three invalid BLOB files which are corrupted PDF's and do not work.

If I try to load up this submission as a PDF, before or after I've edited it, the system fails and I get nowhere....

Using Mac 10.11 Firefox v.71

any ideas? I'm about to give up and find another similar provider.

I wasn't able to replicate the issue when using Windows, so I think the issue is with the Mac's PDF Viewer. 

Could you please try using an Adobe Acrobat Reader to view the PDF files and see if that works?

Related Article: https://support.mozilla.org/en-US/kb/pdf-files-are-blank-or-cause-error-message-mac