Right clicking urlbar results currently doesn't have an effect, so a context menu could be added that has the same items as the new urlbar result menu. As a bonus, it might also provide more freedom for users to remove the urlbar result menu, if the possibility continues to be supported for those who want Tab/Shift+Tab to function like ArrowDown/ArrowUp in the urlbar.
I'm not convinced duplicating the functionality is a good choice, unless there is a use-case that calls for it, and I'd not consider hiding the button a valid use-case since userchrome hacks are not officially supported. It requires UX input anyway.
I want to right click for the menu too, but the reason is that the button is small and the result entry is much larger. It's easier to position the mouse over the entry than the button.