Didn't have usability issues, but found that traffic is not encrypted between my machine and the service if a request it using an IP like http://36.215.234.124/login. I can see all my plain HTTP traffic in Wireshark. It seems to not be proxied.

Looks like a major flaw as soon as it claims to give privacy.

Version used: 2.12.4

PS: Extension in Chrome seems to work just fine in this sense.

For those whom may concern: if you are ready to sacrifice usability to solve this issue you can use another Firefox proxy extension and set up HTTPS proxy there using one of the NordVPN hosts and port 89. This will use encrypted channel