Editing cookies doesn't work (I clicked Add / Edit cookie, Copy last selected, wrote my value and hit save, and nothing happened. Cookie still bears the old value), UI is crappy and user unfriendly. Definitely wouldn't recommend for anyone looking for replacement of legacy but well working https://addons.mozilla.org/en-US/firefox/addon/cookies-manager-plus/
EDIT: To adress author's comment - I mean the value of the actual cookie. It doesn't update in interface neither touches the cookie at all. It still has the value that it had before I tried to edit it (tested with my own website).
I suggest you to fix the bugs, make standart addon interface - a window rather than HTML page (So I don't have to type the adress myself, but just click the button on the page where I want my cookies displayed). Then I will gladly change my rating and will happily use this addon. Until then, disabled.