This extension is awfull. The VPN itself is good, but when I enable this extension on firefox I lose my conection until I disable the VPN again. The Windows app works fine, but I don't want to use VPN on the whole system.

Gets stuck a lot. Sometimes requires a https login for some proxies. The speed is very good, no ip leaks. But the extension by itself is a problem.

Win10 Professional

Pros:
It's useful when it works.

Cons: (all intermittent problems)
After turning on my PC Firefox cannot access anything until I've disconnected and then reconnected NordVPN.
When I try to change locations it sticks at loading servers and never progresses beyond that.
After powering on the PC, NordVPN has logged me out.
Logging in is a pain, I can't copy and paste my username/password because as soon as I click away the login window closes.
I've paid, so I'm stuck with it.
Nordvpn support is quick to respond but their answer is just a workaround (remove/reinstall the add-on). I did that and 2 days later the server load fault is back.
It has now been a month (longer for others) with no progress on the reported faults, dropping to one star.

It doesn't keep me logged in

UPDATE: If you want to purchase NordVPN for the Firefox browser Extension, SAVE YOUR MONEY. It is very frustrating and support wasn't helpful.

This extension has been problematic from the start. It took a lot of farting around to get it to work when I first installed it and for whatever reason it logs out for no reason. NOW I can't log into it and if the extension is enabled none of the websites will load and you are presented with "Unable to find the proxy server". Disabling it then enabling it doesn't resolve the problem nor does restarting Firefox. To make things worse support.nordvpn.com is useless, I can't find any information on the extension for Firefox and it does not provide any way of contacting NordVPN Support. I moved to Firefox for privacy/security reasons and signed up with NordVPN for the same reason, I think it is time for a refund and go back to PIA.

It's working on chrome but not on firefox