JabRef version JabRef 5.0.0-dev--2019-10-25----681d6aa6f
Linux 5.0.0-37-generic amd64
Java 12.0.2

• I have tested the latest development version from http://builds.jabref.org/master/ and the problem persists
  (Nope haven't had the time to do so)

Steps to reproduce the behavior:

1. Import en entry into the database (via JabFox)
2. Right click on the full-text URL and select Download file
3. The downloaded file doesn't have a file extension

Expected behaviour: The file should have the file extension .pdf
Actual behaviour: The file ends with a dot and no extemsion (e.g. test. instead of test.pdf)