This add-on is an absolute must: it speeds up browsing by improving page loading times, and Decentraleyes improves privacy by loading resources from the local system and not from remote locations. Remote sites sites may drop cookies on your local system. They may also record your Internet activity since you connect to them using a web browser, and get information out of those connections such as your operating system, the web browser you are using, your IP address or location in the world.
Support from the developer, Thomas Rientjes, is excellent. There is a good description on the Mozilla add-on page, but when I tried the recommended test utility I got a negative result. A bit surprised and confused I contacted Thomas, and he worked with me until I got the setting right.
To get the add-on working properly, copy paste the rules into uBlock as shown here https://git.synz.io/Synzvato/decentraleyes/wikis/Frequently-Asked-Questions#for-umatrix-and-ublock-origin-non-easy-mode-users
For an independent review of the add-on see the write-up by Martin Brinkmann of the prominent tech website Ghacks.net here https://www.ghacks.net/2017/08/29/firefox-57-decentraleyes-add-on-is-compatible-now/