Installed JabRef v.4.3.1 on Mac Mojave 10.14.2; the installation completes without issues.
JabRef becomes unresponsive once I try to open an existing bib file.
I reinstalled twice, and this behavior repeats each time.
Please try the latest release, JabRef 5.0
This is a new major release, so please be aware of breaking changes. It’s useful to keep a backup of your bib file.