Fennec: add context menu new item to history entry at recent history page

I’d like to add “Forget about this site” context menu item to history page in Fennec. But I am stuck at adding a context menu to a simple image or a link. According to https://developer.mozilla.org/en-US/Add-ons/SDK/Tutorials/Mobile_development sdk/context-menu isn’t supported on fennec, so (if I understand correctly) we have to manually add menus as described here:
https://developer.mozilla.org/en-US/Add-ons/Firefox_for_Android/API/NativeWindow/contextmenus
But this method doesn’t work for me on fennec version 39 and 40a2. (Haven’t tried with older versions.)
Is this page outdated or is there a bug?
This extension:
https://github.com/canuckistani/fennec-plus doesn’t seem to work for me on fennec 39 and 40a2).

Can you give any hints? Or, if you know, is there a more simple way to add “Forget about this site” to fennec? Or maybe there is a ready extension I don’t know about?

Fennec is firefox for android right?

Its very easy to add to context menu: https://developer.mozilla.org/en-US/Add-ons/Firefox_for_Android/API/NativeWindow/contextmenus

Or add straight to the main menu: https://developer.mozilla.org/en-US/docs/Extensions/Mobile/API/NativeWindow/menu