The goal is the same as https://issues.jenkins-ci.org/browse/JENKINS-61092 but for the maven-frontend-plugin instead of the maven-karma one.

The major difference is where the karma plugin overload the karma configuration of the projet, to add the requirements for JUnit compatible XML outputs, thus knowing where these reports will be, the frontend plugin does not alter karma configuration. So you have to add what is needed yourself, and thus the output directory is only known by karma, not the plugin, so not exposed ...