I'm curious if anyone knows of any standards related to Outlook clients and dragging mail items to CRM using the "Drop files here to attach them" button.

My tests are pretty divided.  Outlook 2013 doesn't work with firefox, yet works with chrome and edge.  Outlook 365 doesn't appear to work at all, the button lights up but upon release nothing happens.  Perhaps there is some sort of standard or security permission they may have run into that blocks the functionality from working?

While desktop dragging works for any browsers.