Cross-origin (CORS) error from my Firefox browser when I run pdf-lib

[RunHot]

I'm having trouble running pdf-lib. I get the Firefox browser error listed bellow when pdf-lib tries to access my existing .pdf file in order to modify it:

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://www.dropbox.com/s/n7n49vhh1noryi7/Certificate%20of%20Residency.pdf?dl=0. (Reason: CORS header ‘Access-Control-Allow-Origin’ missing). Status code: 200.

This is my first time running pdf-lib, so I'm guessing there's something in the docs, I'm not understanding. The .pdf file is hosted at Dropbox.com.

Thanks for any help 🙂