It was great addon (and it still is) up to v4.9 for my Firefox 56.0.2. After that release all next releases are crap - they are completely not working in the same Firefox 56.0.2. After updating of this addon all my lists of words are gone. I click on + to add a words - and nothing happens. Clicking on other buttons doesn't work too. Addon completely dead and mulfunctional.