The "browser.bookmarks.editDialog.showForNewBookmarks" preference is equivalent to the "Show editor when saving" checkbox that is on the pop-up dialog.
This is typically due to third-party software that has somehow been installed on you machine, typically called adware. Try using a product like Malwarebytes to remove it.
The tag option is now not displayed by default unless you've tagged a bookmark, i.e. if you have at least one tag in the bookmark manager, then you'll have tags on the new bookmark pop-up.
