Did you try to recreate the bookmark in private the same way you did it before and see what it does?

Thanks for your time! Unfortunately it didn't do it. And this is what I did: Removed the bookmark, visited the site in a new private window, added the bookmark, closed the private window, opened up a new tab, clicked the bookmark, it visited the site just like normal i.e. not in a new private window (quite expected that). Edited the bookmark and tried adding both private://# and private:///# in front of http://www.example.com and trying them in between the edits, of course.

As mentioned, this could have been an addon feature, my memory is bad. You see, Quantum had trouble starting after the upgrade today. I know the addon API is very different so I though "well f*** it, I erase my damn addons and live with it" so I didn't think of really checking all my addons. (My bad entirely and I usually have a better judgement...) Then it turned out it was not any addon causing the problems, haha in my face! Aaaany who; I tried looking up addons that do this, but to no avail at the time. As ar as I know one can't google "private:///" even with the qoutes...that probably would have found the addon if it was possible.

This feature was likely added by the Legacy extension Private Tab that no longer works in Firefox 57+.

• https://addons.mozilla.org/firefox/addon/private-tab/
• https://github.com/Infocatcher/Private_Tab_WE#issues

Thanks! Could have been that one.

I'd be glad to see it as a native feature as said. Guess I'll have to just wait until it is somehow possible again.

While this "problem" isn't exactly solved I'm still satisfied for the time being and mark it as such.