We apologise that the Firefox version of Kopernio cannot export the PDF with the reference to Endnote from the PDF Viewer. A fix will be available within 2 months for Windows and 3-4 months for MacOS.
In the meantime, there's a way around this issue.
Please click the "Download PDF" button, instead of "Export Reference", and then open the PDF with EndNote.
You might need to update your browser settings, to see the "Open" dialogue:
Let us know if you need any help or if you have any questions. Please email us at firstname.lastname@example.org.