It works (using Firefox 59.0.1 and version 2.1 of the add-on)

Do not know too why the addon has bad reviews. I rate it for 5 stars. Works perfect! / Не знаю, почему аддон имеет плохие отзывы. Я оцениваю его на 5 звезд. Работает отлично!

I see all these bad reviews, but the add-on works, I go to twitter, find a video or a gif, and I can hit "Download" to...well...download it, does exactly what it says, can't see how this is 'spamware'