The problem with uMatrix is that many sites that rely on third-party Javascript will silently fail (i.e., not load, or show a "loading" animation that never ends), so you need to remember to turn it off for such websites.
It helps if you open uMatrix every time, see what third-party CDNs are used, give them necessary permissions but not more (only images if they don't need a script, no cookies unless it's necessary, etc), and put them in the whitelist. It's a bit of work in the beginning but after a while almost all new pages you'll come across will run fine.
