MacOS – Disable font anti aliasing in Firefox in OSX

You could open a terminal window and change to the network path so that the file system is marked as in use. You could also open a file or application on the drive.

The users might still choose to force eject, so it's not a proper ban on ejecting the volume, but it adds another roadblock.

Try this

tell application "Firefox"
    activate
    tell application "System Events"
        keystroke tab
        keystroke (key code 125)
        keystroke (key code 125)
        keystroke (key code 125)        
    end tell
end tell

You might not need to activate Firefox if it's the current active app. Them you just need :

tell application "System Events"
    keystroke tab
    keystroke (key code 125)
    keystroke (key code 125)
    keystroke (key code 125)        
end tell