Hi nashe,

I'll see about getting some screenshots and a better description out. When you click the button, it should darken the web page you're looking at. When you click on the page, the first click will start a box and the second will end it and you'll get the pixel dimensions of the covered area.

I've seen a little bit of flakiness, but so far I can't reproduce. For example, I loaded facebook, clicked the button, and nothing happened. Then I went to Yahoo and it worked; back at Facebook again it started working.

If it's nothing too private, can you share what site you were on when you clicked the button?

Also note: According to https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Your_first_WebExtension#Testing, this kind of extension is disabled on addons.mozilla.org, so if that's the only place you tried it, it won't do anything.