RIDICULOUS decision.
A free addon for paying users.
Who on freaking earth, heaven and hell came up with this amusing idea?
And they don't even write it clearly in the short description right next to "add to firefox", which is as far as most of us go when downloading something with a good reputation.

Seriously, who can be so greedy and mean to make such an addon only available to paying users?
Another famous VPN also offers 10GB free monthly and they offer an addon for everybody.
It totally makes sense.
There are already enough downsides with the free account. Let people use the app, so they can see if they like it. Not everybody wants a system wide VPN!

So not customer friendly.
And their people in Reddit even removed my post when I was asking about this.
I swear I will never pay for anything Proton now. EVER.