Sort of functional, but the user interface is pretty bad.

You can search for cookies, but only if you already know exactly which cookie you're looking for. E.g. if you know that cookies have a "host" field, you can enter an exact name there and click "search". It only finds exact matches (no substring search) and there is no autocompletion. The UI form is spaced out all over the window, so you might not even see the buttons at the bottom at first glance. As far as I can tell, you can't really edit existing cookies. There's a "new cookie" form (which completely replaces the view/search form, you can't have both open at the same time) and its fields always start out empty, even if you had an existing cookie selected before. Even if you've managed to create your own cookie by filling all fields and clicking the "save" button, there is no apparent way back to the overview screen. The "new cookie" form just stays open and sits there. Fortunately the "cancel" button doesn't actually cancel your new cookie but takes you back (?).

3 stars because the add-on technically works (I think?), but the UI is borderline unusable.