All computers today can have multiple user accounts. Unless the user is listed as an administrator, the user has access only to their own account.

If others are using your computer, set them up with their own accounts on your system.

My PC at the office is sometimes used by others, and they frequently access mutually used web sites using my saved info. I'd like to prevent others accessing all my saved sites, info. Seems to be logical, but I'm unable to figure it out. Thank you.

What type of information? bookmarks, passwords . . . .

Private Bookmarks https://addons.mozilla.org/firefox/addon/webext-private-bookmarks/