Rated 5 out of 5 stars

Από τον/την Χρήστης Firefox 5c7776 στις Νοέμ. 19, 2017 ·

doesn't work on new firefox ;/

από τον Oleksandr (δημιουργός) στις Νοέμ. 19, 2017 ·

Unfortunately, WebExtensions (the new API for Firefox 57+) does not have the functionality for the correct operation of this addon in Firefox 57+.

But you can install Firefox 52 ESR and enjoy work until June 2018
https://www.mozilla.org/en-US/firefox/organizations/faq/