It usually doesn't work.

Did not work. Kept receiving the same data for every website - even after restarting MFF and PC.

Doesn't work all the time. If you want a more reliable tool, check out the "BuiltWith" extension by garazy.

This Addon send every url you visit to there Server.
You don't have to click on the button for that.
There collect your Browser-History.

Does this add-on send data/query to whatruns.com on every page I browse? Or only when I click its toolbar button?