Sadly, a case study as to why to not enable automatic updates. Clippy and Louis Rossmann would be sad. Created an account to review due to recent changes.

I will give the author credit where it is due, he seems to be updating the extension regularly. It's now on version 3.31 and as far as I can tell, the subscription wording was added back 3.29, and I've since downgraded to 3.28 and will leave it there until I find a replacement. I will also give the author credit for creating a popup to let me know as I hadn't realized it had stopped working. And I learned that downgrading an extension is a built in feature of Firefox.

The only other extension I know that charges is PushBullet, but their free option is quite more generous than '3 times a day.' I also rather look at it that something has changed for the developer as he now feels he needs funds and hope things turn out well for him. It's easier to think that, than something like he just got greedy. Or maybe it's better the other way around?

For what it claims, it seems to do what is says. Only had some issues with locally hosted sites, but the blacklist feature is useful enough for that.

Edit:
Updated to 2 stars due to friendly developer response. I cannot go farther than that because they change the extension after the fact. Would have no issue if it was like that from the start. It's unfortunate because I see where the developer is coming from (as a programmer myself) and I understand the thought process, but can't support the act. If you see this Francisco, I thank you for your offer, but I'll have to refuse on principle.