I did not install the plug-in.

As a privacy-conscious individual, it concerns me that this extension requires the "Access your data for all websites" permission. This seems suspicious and unnecessary, given the technical details of how the internet works and the Firefox documentation.

It appears that blocking websites is doable without the "Access your data for all websites" permission, as suggested by the existence of the "Liberty Arrow" add-on by Gary Strivin'.

Wow.. this one simply blocked facebook.com for me.. saved me tonnes of productive hours.. highly recommended!