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!

This could be so freaking good. But ... it can be a real pain in the ass! Why? Because sometimes just having uMatrix enabled in the Extensions page of Firefox will break some websites even though uMatrix is set to "Disabled for this scope."

This occurs mostly on login pages, and one has to go to the extension page and disable uMatrix to login to a site. This is across both Linux and Windows.

If there was a way to COMPLETELY disable uMatix from the toolbar... well that would be great.

Great replacement for NoScript, thumbs up!

I really like that you can block everything within one add on. I am still learning how to use it. Two things would be great to add:
1. I would like to be able to import my old NoScript whitelist.
2. NoScript had a feature that you could middle-click on a domain in the dropdown list and you could customize to go to another website:
I had it so I could quickly check that domain on Norton, like this:
https://safeweb.norton.com/report/show?url=someSite.com
It would put "someSite.com" (whatever you middle-clicked on) on the path
so I could easily know whether to allow that javascript for someSite.com, etc.

too much puzzle to get the right attitude, so that get the one to see the things that are needed on a site

Thanks Mozilla for breaking NoScript. Wouldn't have found uMatrix without it. With NoScript, I essentially had to reload pages to Chrome to get 'em to work. Now I can SEE what exactly is going on and give permissions as I need to.

I'm using block all / exceptions. https://github.com/gorhill/httpswitchboard/wiki/How-to-use-HTTP-Switchboard:-Two-opposing-views is definitely required reading.

Addon poderoso que bloqueia solicitações de conexões indesejadas, conforme o próprio desenvolvedor, é para usuários avançados, mas nada impede que você se adapte aos poucos e aprenda muito do que acontece "por trás das cenas". Hoje, para mim, é indispensável e insubstituível. Eu poderia ficar sem qualquer outra extensão para privacidade, uMatrix supre todas as necessidades que tenho. Ainda estou aprendendo. Perfeito !

I've been using ad-hoc blocking methods in different addons for some time. uMatrix combines them all very neatly and conveniently. (And it's now on Android too!)

Brilliant!

THE BEST OF THE BEST IN THE WORLD....POINT !

it's for something that understands networking and how internet, DNS, SOA and all related things !