Rated 2 out of 5 stars
Worked fairly well until after 4 days of use, I too am getting the "Subscription Expired" error. The add-on was downloaded from addons.mozilla.org.This review is for a previous version of the add-on (188.8.131.52-signed).
Update timing issues
We've had few intermittent server problems - if the software checks the server and it's down, you might see this error - we're working on fixing this.
Meantime, simply wait 1 day or download again and this problem should disappear.