Homepage settings

Firefox forum and browser has nothing to do with how you set your opening homepage other the url set to the homepage when it opens. If your having issues maybe you should password protect your system so no one can use it unless it's you.

How to set opening homepage to private viewing

https://support.mozilla.org/en-US/kb/private-browsing-use-firefox-without-history#w_can-i-set-firefox-to-always-use-private-browsing