As per our correspondence and per the add-on description, the add-on features will appear with the context menu. The context menu appears once one uses right-click (or control-click for one-button mouses).

Firstly, while I've added some code which should better ensure the existing context menus upon uninstall, in my own testing, this was already occurring. This is typically handled by Firefox itself in the case of a WebExtension (which this is).

Secondly, I've implemented the ability to copy from a text box (inputs and textareas), and a new version is awaiting approval to also allow copying link text or URLs.

In the future, unless an add-on is actually damaging your data, I think it's better form to contact the developer before giving strongly negative reviews, particularly for free/open source code...