ps -xc|grep -sqi firefox && osascript <<'APPLESCRIPT'
   tell app "Firefox" to activate
   tell app "System Events"
      if UI elements enabled then
         keystroke "r" using command down
         -- Fails if System Preferences > Universal access > "Enable access for assistive devices" is not on 
      else
         tell app "Firefox" to Get URL "JavaScript:window.location.reload();" inside window 1
         -- Fails if Firefox is set to open URLs from external apps in new tabs.
      end if
   end tell
APPLESCRIPT