Rated 4 out of 5 stars

Good. But needs more flexibility (a one-click way of adding exceptions to monitoring). The cleaner is good. Sadly, no way of getting its own button easily onto the toolbar. Recommended!

This review is for a previous version of the add-on (3.5.1-signed.1-signed). 

Thanks for your feedback, you are indeed right and therefore such a one-click solution has been implemented, feel free to help betatesting it by installing the new version from the Github repository at https://github.com/diegocr/PrefMon - which you can do by using the GitHub Extension Installer Add-on: https://addons.mozilla.org/addon/github-extension-installer/

Kind Regards.