I did in fact contact Mendeley and the person helping me there in the chat did not have the same problem. I sent him the url and he sent me a video of being able to save the pdf to mendeley. He suggested that I add the url to trusted websites but that did no change. It seems to be a bug on the firefox end and not mendeley. Does anyone have any other suggestions???

This used to be a very useful add on for university students but has lost a great deal of it's function due to firefoxs "blanket ban"

For a few years now, Firefox does not allow any add-ons to inject code into the built-in PDF Viewer -- it is a privileged page. For example, this prevents highlighters from working because they need to modify the page.

I don't have this add-on, but saving the entire PDF to an external program sounds like it should be possible because the add-on doesn't need to modify the page to re-download the file or grab its URL.

I took a look at https://addons.mozilla.org/firefox/addon/mendeley-web-importer/

Are you trying to save a link/reference from within the text of the PDF? Unfortunately, that doesn't work.

As a somewhat clumsy workaround, you can save the PDF locally, then load it into this web-based viewer:

https://mozilla.github.io/pdf.js/web/viewer.html

That actually is the PDF viewer that forms the base of Firefox's built-in viewer. See the attached screenshot for reference on the load button.