Using e.g. chromium, some PDFs can be read in the browser, with the URL of the PDF staying in the address bar e.g. http://www.africau.edu/images/default/sample.pdf, and some other can only be downloaded, then shown in the browser when they have been downloaded, e.g. https://www.ru.nl/publish/pages/769526/mark_vink.pdf will be downloaded then displayed with address file:///home/user/Downloads/mark_vink.pdf, after it has been downloaded.
Why is that?
I'm asking because it seemingly breaks the workflow for the Zotero Connector extension: PDFs that have been downloaded cannot be imported in Zotero, while the ones that are displayed (with the remote address) in the browser "natively" can be imported.