The best way would be to use the firefox inspector. Open the page, press F12 then choose Network or Ctrl-Shift-Q to start the Network inspector directly. Then reload the page to see all of the network requests made, times, etc. Far more detail than you likely need.
If you want a lower-level command-line display, you'll want to look into netstat. You can filter by process id. For instance, sudo netstat -ptc | grep FIREFOX_PID will show all of the connection firefox makes, refreshing continuously (c). Not very useful though, lots of noise.