For instance, I like the inspector much better as it has vertical/horizontal lines which helps with alignment. Also I like the new (Firefox 52) "invisible" text nodes feature.

Overall, I like the (dark) theme UI/UX better, and also the DOM node hightlighting better.

The eyedropper and the full page screenshot tool are great too (do not know if Chrome also has it). And using all these tools from the devtools command line: https://developer.mozilla.org/en/docs/Tools/GCLI

There are drawbacks like the new debugger which is missing a lot common tiny usability features currently (making it hard to use) - and it's still buggy. But it's rewritten from scratch using modern technologies like react/webpack. So it's evolving fast.

Edit: Fixed typos.