WHY ISN'T IT INSTALLING? Rated 1 out of 5 stars

I've used StumbleUpon ever since I stumbled upon it & I got a new computer & I've been trying to download it, it shows installing, but then I can't find it. What happened? Is it gone or is there a new name?

This review is for a previous version of the add-on (4.14.1-signed).