I upgraded to Debian 10 and no longer can I start JabRef. The original default java was 11, i did update-alternatives --config java and selected version 8, then the commands below followed.
user@local:~/.local/jabref$ java -version
openjdk version "1.8.0_212"
OpenJDK Runtime Environment (build 1.8.0_212-8u212-b03-2~deb9u1-b03)
OpenJDK 64-Bit Server VM (build 25.212-b03, mixed mode)
user@local:~/.local/jabref$ apt search openjfx
Sorting... Done
Full Text Search... Done
libopenjfx-java/stable,now 11.0.2+1-1 all [installed,automatic]
JavaFX/OpenJFX - Rich client application platform for Java (Java libraries)
libopenjfx-java-doc/stable 11.0.2+1-1 all
JavaFX/OpenJFX - Rich client application platform for Java (Javadoc)
libopenjfx-jni/stable,now 11.0.2+1-1 amd64 [installed,automatic]
JavaFX/OpenJFX - Rich client application platform for Java (native libraries)
openjfx/stable,now 11.0.2+1-1 amd64 [installed]
JavaFX/OpenJFX - Rich client application platform for Java
openjfx-source/stable,now 11.0.2+1-1 all [installed,automatic]
JavaFX/OpenJFX - Rich client application platform for Java (sources)
user@local:~/.local/jabref$ java -jar JabRef-4.3.1.jar
Error: Could not find or load main class org.jabref.JabRefMain