After creating your bookmark, if you click the blue "star" in the address bar, Firefox should drop down a panel that lets you change the folder.

At the bottom, there is a checkbox to "Show editor when saving" so you get this panel automatically in the future.

Does that work for you?

ok, but I this wasn't necessary in advance before latest update

I don't know how that box got unchecked. Once it is checked, it should work the same as before.