Remote Access? Quick Access? What operating systems are you using? Do you have full administrative rights to your friends computer?
What messages or errors are you getting?
Most likely it would be easier for your friend to just download and install Firefox directly. By adding in "remote" connectivity you are just adding more room for errors and problems.
I am not what size the install package of firefox is, but from my understanding it just launches and then reaches out to the internet. You may be able to email him the file. Or Start a One Drive or Drop box account, place the package in there, then have him copy it from there. I am not sure why they can't just download it directly. Other option would be to download it to a Thumb Drive and then mail that to him.