It exists for Chrome and Firefox. It has access to all sites you visit, and collects everything you do.

Over 600,000 Chromium users have it installed.

What made them to install this ?

They don't actually know how much this is collecting. It advertises other features like site rank https://i.imgur.com/qfitydx.png

Whoa are browser toolbars still a thing? I thought they became irrelevant over a decade ago