Hi, do you mean when saving a new bookmark?

First, Firefox has switched to always saving new bookmarks in the last folder you saved in, so once you choose Bookmarks Menu, that should stick.

Second, after saving a bookmark, click the blue star and make sure the "Show editor" checkbox is checked so you can check/change the folder before saving the bookmark:

Was that what you needed, or still not working quite right?

Or if you meant that you only have the "Library" button () and not the Bookmarks Menu button () on the toolbar:

You can add that button using either:

(A) Use the Customize panel (Customize Firefox controls, buttons and toolbars) to drag the icon to the desired spot on the toolbar

(B) Use the method from Bookmarks in Firefox - section entitled: How do I add the Bookmarks Menu button to the toolbar?