Sorry Mozilla doesn't have anything like that for Firefox bookmarks, and I have never seen an extension which adds a feature like that to Firefox.

Firefox does have the ability to have multiple user Profiles, within each Logon User Account. And each LUA automatically has its' own unique Profile.
https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

Plus - Windows has Logon User Accounts for privacy such as that. Every user account has a separate storage space for user data.

Personally, I would worry more about "others" having access to my passwords while using my web browser, rather than limiting access to a folder of bookmarks.

Just save them in an HTML file and open this file in a Firefox tab when you want to use them.

The only safe way would be to try this. Create a text or doc file. Put all of the addresses and anything else you want to protect in it. Then use a file compression program using the password option. Once the program is done, open the new file without the password, then with the password. If it works, then delete the old files and keep the password protected file. Remember to clean out your recycle / trash can. And above all else, Remember The Password!! Later, when you need the information, open the passworded file. Then use the copy / paste to move the information to the browser. BTW, Firefox will automatically record where you have been in the history files, so remember to remove that information. Check out Firefox Private Window.