What do you have set here? see screenshot

Let's say you open 3 tabs and close two. Firefox may not terminate the content processes used for the closed tabs because you likely will open some more tabs during your session. At least, that's the theory. Also, some tabs are used for the browser itself.

thank for answering. hope you are having a merry Christmas.

It is quite normal to see more Firefox processes running.

• one process for the main Firefox thread (user interface)
• one or more content processes, see:
  Options/Preferences -> General -> Performance
  remove checkmark: [ ] "Use recommended performance settings"
• a process for the compositor thread
• a process for the WebRender when this feature is enabled
• a process for extensions

You can find the current multi-process state on the Troubleshooting Information page (about:support).

• "Help -> Troubleshooting Information"
  "Application Basics": Multiprocess Windows
  "Remote Processes" further down

See also the about:memory page for information about the process IDs.