To install FormReturn on linux, you need to be sure you are running Sun's version of Java 8 at minimum or a recent version of OpenJDK 7.
Once you have installed java, make sure you remove any references to other versions of java such as GCJ.
Then, either launch the jar file by running it using the sun launcher (right mouse click on the jar file) or do the following from a terminal shell:
java -jar formreturn_setup_(version).jar
Simply follow the prompts to install. Once the installation process has finished, you will be able to launch FormReturn from your ~username/FormReturn directory by running ./formreturn.sh
If you are using Unity, you can go to the FormReturn folder and drag the program icons to your launch bar.
To uninstall, remove the FormReturn directory and also remove the .formreturn directory from your home directory.