A proposito de iste extension

Usage
Simply hold down the SHIFT key and scroll with the cursor over any part of the page.

Limitations

Due to mozilla's security policy, add-ons not like this one are not loaded in most of the internal pages of the browser, so it will not work there.
The browser should be in the foreground
The cursor must be on the page, and the page must have finished loading

Evaluta tu experientia