Find the names by examining the files in /usr/share/dbus-1/services/. You need to look at the line Name= in each file and ignore the com.nokia at the start.

fennec is called mozilla.fennec, so it cannot be executed by the osso_exec function. You need to copy the four lines in osso_exec definition and replace com.nokia.+name and /com/nokia/name with mozilla.fennec.

mediaplayer is another issue, since executing it just runs the background process. You still need to find out how to make it open a window.

You don't need to reboot after editing the script, since it is executed at each key press.

Note that it is a python script, so white space is important, etc.

You can debug your changes by running from the command line

/usr/bin/keyboard-shortcuts a b c d 198

where a b c d are any four parameters (ignored by the script) and 198 is 192+ the letter you wish to emulate (198 being f).