Clicking the toolbar icon does the following:
It marks the domain of the active tab untrusted (full blocking or half), reloads the page and blocks scripts from running on it. An option for the user to stop a website eating up resources or doing malicious things even if it breaks the functionality of the page.
It is the complete rewrite of the YesScript addon that will be incompatible from Firefox version 57. Currently available for Firefox browser only, see the official addon page for more info:
https://addons.mozilla.org/addon/yesscript2/
I take no responsibility whatsoever in regards of this software, use it at your own risk.