When you download a simulation file with a .hoc extension you can automatically run it, ie., NEURON will run in a new xterm window and execute the .hoc file. When you quit the simulation ((control)d in the xterm window) the xterm will go away.
Warning: There is no security with this feature since .hoc files can execute arbitrary shell scripts. If you do not install it you can always download the file into some name, examine it, and then execute it explicitly with NEURON.
You need to edit two files in your home directory: .mime.types and .mailcap
Add the following lines to $HOME/.mime.types
application/neuron hoc
Add the following lines to $HOME/.mailcap
application/neuron; mos2nrn %sThe mos2nrn script is found in $NEURONHOME/bin