It is working fine (Firefox for Mac): fast, lots of servers, specialized servers.
WebRTC Prevention included.
Sometimes got a connections error, this usually happens after a Firefox update. Solution: logout and login again or reinstall the add-on

Request:
A "Favorite Servers" menu like in the Desktop Application

PS:
Yes it is a paid service. You can buy a Lifetime Subscription here: http://bit.ly/2GkBzbu

UPD: Addon is annoying as hell.
Adding to the last review:
4) Frequent connection losses and NO WARNING! Ffs, devs, it affects privacy, you know? Plugin just breaks connection and you continue to work through the censored compromised government network. Great, just great!!!
5) "Like our app"? Constant, never ending notifications to rate and review. Even "never ask again" does not work. You want review!? Get it!!! Spend some time to update this addon, it is horrible and annoying!!!

(last version)
It's ok, but not ideal.
1) Plugin asks for password sometimes when you reopen browser. Don't have option to save it somehow.
2) Plugin does not remember the connection status. So upon browser start you have to turn the vpn manually. Even with "Auto connect" option turned on.
3) The most annoying thing is that it often loses your chosen country and sets to "Optimal server" which is usually (surprise!) the same country as yours. Guys! VPN is used exactly to go through other countries, I don't need my homeland's censorship, even if it's "optimal". It's just stupid.