This is the best Firefox add-on ever!
In my opinion should be a must, a FF built-in.

I read that the author uses UBlock, rather than UMatrix. It is not my case, and would like to share my logic:
UBlock is a great add-on too. However, if you use a more friendly granulated firewall (UMatrix), you avoid most of the ads, trackers, scripts etc. Doesn't make sense to use a more generalist firewall (UBlock), and at the same time having to add lot of filtering hosts/lists that reduce browser performance. The main filter should be the firewall itself, rather than the hosts/lists.
UMatrix well configured will block most of the stuff, without adding hosts/lists, and increasing browser performance.

Some users say that UMatrix "is difficult to understand, to learn, to configure etc", but this is not true.
The problem is not the add-on, but the user! Users don't want to read, to learn, to understand, to configure etc... they just want to install & use. The point is that UMatrix-wiki doesn't take maximum more than 15 minutes to be read, and another maximum 15 minutes to learn how to use it. Considering that UMatrix will work like 3 or 4 different add-ons at the same time, I prefer UMatrix taking me 30 minutes, rather than 4 different add-ons taking me 60 minutes or killing the browser performance.
And those users complaining about UMatrix breaking this or that... seriously... or they don't know how to use it, or they want the impossible (a firewall that blocks everything without blocking nothing).

My dream and request are:
1) A simple "disable option" at the main-panel, without white-listing (it is very unpractical to do it trough FF add-on page).
2) A real-time cloud malware/antivirus/phishing/ransomware etc service option.
3) A blocking ads and trackers/tracking not by hosts/lists, but by encoded rules (like "BluHell", "Privacy Protector" etc).
4) Same UBlock dashboard options in UMatrix dashboard. Another possibility (and perhaps easier) might be making UBlock firewall more friendly granulated as UMatrix.
5) Incorporation of same special NoScript filters, increasing security capabilities in unlocked-firewall.
For this dreamed add-on... I will be more than happy to make a fat donation!

Thousand thanks to the author!