If you've obtained a JAR file that is not available in an existing Maven repository, you can add it to your local Maven repository with the following command. Make sure that all of your options are surrounded by double-quotes:
mvn install:install-file "-DgroupId=org.mozilla" "-DartifactId=jss" "-Dversion=4.2.5" "-Dpackaging=jar" "-Dfile=jss-4.2.5.jar"