Firstly, Firefox will keep a history of the recently closed tabs, even when you are using Firefox in Private Browsing mode. It's a common misconception that Firefox doesn't store any data when you are using Private Browsing mode.

In fact, Firefox will still save recently closed tabs, cache, cookies and stuff like that in Private Browsing mode. The difference from regular browsing is that once you close that Private Browsing session, that data is erased.

As for the tabs listed being from websites you didn't visit, it's possible that a website or another program on your computer opened the tab for a split second and closed it automatically. In that case, it's likely that the tab would appear in the recently closed history, but it's unlikely that you would have visually seen the tab open and close so fast.

It depends on what the websites are. If they are ad websites or other sketchy websites like that, this is the likely cause.

Hope this helps.

Mr. Brantley, Thank you for your response answering my query. I now am aware of the reason a website may have been visited without my direct request.

Unfortunately for me, I continue to be perplexed by the concept of Private Browsing. I am not requiring additional input in response to my confusion, the following is a comment explaining what confuses me.

Specifically, if the purpose is to stop other users of this device (in this case Laptop) from ascertaining my activity while in Private Browsing Mode, isn't it counterproductive to be detailing that activity in the closed window history? According to the Firefox article which explains the Myths of Private Browsing the following is described;

"Myth 2: Private Browsing removes all traces of your browsing activity from your computer. Reality: Private Browsing works by removing cookies, browsing history, and passwords stored while you are browsing once you close your Private Window. If you download a file from a website it will remain on your computer, though it will not appear in the download manager in Firefox. Also, if you bookmark a site while in a Private Window, it will remain in your bookmark list. Myth 3: Private Browsing doesn’t display any browsing history. Reality: Private Browsing will, by default, display visited sites and bookmarks as you type in the address bar. These are the URLs saved to Firefox during normal browsing."

I am confident that your response is accurate, but it leads me to the conclusion that the intended purpose of Private Browsing is also a myth. I am probably missing or misunderstanding the information which lead me to this conclusion. If you believe you could explain why my conclusion is flawed I'd appreciate your input. Either way, I accept your answer to my original question. Thanks again!

The way Private Browsing mode works is that all session data is kept in memory during the entire PB mode session and isn't stored in your profile folder. There are misconceptions about cookies, but you wouldn't be able to use a lot of websites when all cookies would be disabled and websites could easily detect whether you use PB mode. PB mode has nothing to do with cookies or history or websites detecting your IP, but is only about not storing persistent data in the profile folder. There is not much difference between regular mode and PB mode when it comes to cookies although website that use other types of storage might not work properly (no permanent storage is available). You can disable most features easily in normal mode if you do not want to leave traces in the profile.