You are asking this question quite often...Why not just follow up one of your threads as they obviously are about running forms with firefox?
Anyway; to sum it all up, in order to get firefox running you need to configure the sun java plugin which you already did: http://www.oracle.com/technetwork/developer-tools/forms/documentation/forms-jre-131772.pdf
Then you need to set the jpi_mimetype in your formsweb.cfg accordingly to the version of the jpi you installed. If you want to start forms with any java plugin just change it to
Following should help - no need for firefox or any browser: Just runs your forms stand alone (you can give your clients an executable .jar or a .exe)