Having recently switched to Edge Dev after having used Firefox for roughly a year (and Chrome before that), I'd say Firefox devtools' strongest point are the style editing stuff.

Somehow Firefox devtools feel a bit clunkier when working on JS projects but they offer a lot of neat gimmicks if you dig into the depths of CSS. I also find the guidelines when highlighting an element more helpful than in Chromium for aligning elements on the page.

Personally I don't get to use grid layouts as my code has to work in IE11 (I gave autoprefixer a try but in the end it was no significant improvement over flexbox because of all the caveats and limitations). If you do, I'd imagine Firefox devtools would be a gamechanger for you.

I find myself occasionally switching back to Firefox for CSS work, then going back to Edge Dev for everything else.