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

JabRef version on Ubuntu 18.04

JabRef 5.0-dev--snapshot--2018-09-19--master--d8f6c5cec
Linux 4.15.18-041518-generic amd64
Java 1.8.0_181

Steps to reproduce:

1. Quality
2. Find unlinked files
3. browse
   Then it will stuck. I can move the mouse, switch to other software, but whatever I do to jabref is useless. I can't close it by clicking exit.