• [X ] I have tested the latest master version from http://builds.jabref.org/master/ and the problem persists

JabRef 4.4-dev--snapshot--2018-06-15--master--f47b74066
Linux 4.4.0-128-generic amd64
Java 1.8.0_171

Steps to reproduce:

1. Tools -> New sublibrary based on AUX file
2. Choose a library
3. Click "Browse"

JabRef then hangs. There is no error message. It must be killed and restarted.