Get return values from nsIProcess

Hi, how can I execute a program and get the return values? (twos strings)
I am using nsILocalFile and nsIProcess to do a process.run on my program. But I cannot find a way to get the return values.

Alternatively, I would love to communicate with the executable using some type of pipes instead of command line arguments.

As a contraint, my customer is on Firefox 45.5. (no they cannot upgrade at this time)

Thanks very much for any help.