If installed, remove jna-4.4.0.jar and replace it with jna-5.5.0.jar. This library is only necessary for native, local or embedded connections. If you use pure-java connections (the default), you don't need JNA.
Native libraries will now be disposed on application exit (JDBC-519)
On JVM exit or - if deployed inside a WAR - servlet context destroy (tested on Tomcat), Jaybird will call fb_shutdown on any loaded native libraries and dispose the JNA handle to the native library. This should prevent crashes (e.g. access violation / 0xc0000005 error on Windows) on library unload if there were still embedded connections open.
Given the potential for bugs or timing issues with this feature, it can be disabled with system property org.firebirdsql.nativeResourceShutdownDisabled set to true. This property must be set before Jaybird is loaded, preferably on the Java command line.