it's 3.31.3 release day, upload a tarball and show that our software is more stable than this table 彡┻━┻
In dropping the support for creating website links from Firefox drops, commit 0e0f5b9a also removed the ability to handle _NETSCAPE_URLs at all. Re-add the necessary bits for drag'n'drop downloads to work as they did in GNOME 3.28.
Closes: #687
