I can't seem to make the switch away from Chromium devtools. I don't know whether it's because I am habituated to the Chromium ones or whether there is something klunky about the Firefox devtools that I can't put my finger on.
Speaking for myself, I'm in the other camp. I never really ditched Firefox for Chrome except for a brief period[0]. I returned to Firefox back when it was still called "Firefox (Not Responding)". Other than the renaming (/s), it -- generally -- flies. The devtools do what I need them to do, however, I used to hop back and forth from Chromium to FF a lot more.
So I'll be re-evaluating things, again, myself -- just in the other direction. :)
[0] I used Chrome for about two years after its release because Firefox wouldn't work with an internal application. It was just easier to use a single browser.
Main reasons were speed (Firefox opened slightly slower, and there seemed to feel like subtly more per-character latency typing in URL's) and minor anti-native behavior (the default-disabled-until-you-move-your-mouse Save button was particularly annoying, even though I understand the rationale).
I got the dreaded "Firefox process is already running" dialog a few times and had to close all my windows (ugh). I really missed Session Buddy; tried alternatives like Tree Style Tab but they weren't as clean.
Finally, one or two pages didn't render / operate properly (guessing due to non-cross-compatible JavaScript statement buried somewhere in them).
Unfortunately I don't have the time to create good step-by-step reproducibles and log bugs. I know some of this can be tweaked out via preference settings. I even spent some time tailoring my userChrome.css per suggestions here. But just couldn't get everything to work quite perfect. FF will have to spend some more time as my secondary browser, may give it a shot again in another year or so or next time Google pedals something stupid. Will try out the new devtools when I'm working on a page, maybe that'll be the hook for another attempt.
After deciding that life's too short and that I really should give it a try - I've found out that source maps doesn't work on Firefox's dev tools. Back to chrome.
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.
The only good thing is that when the new Edge enters general availability, we can likely get rid of 100% of our IE11 users for good.
I have the same problem in the opposite directions: the interface of Chromium developer console is unfriendly to me, I never manage to get comfortable with it...
Me too, as one example: Chrome had no way to edit/re-send AJAX requests for the longest time
So every time I stumble upon that I'll open Chromium, find the stack trace and go back.
The debugger/sources view in Firefox also seems buggier still. E.g. a lot of times while it correctly displays source-mapped locations in the console, clicking on those source links will not actually go to the right place in the source view (it will either end up in the packed source or it will not go to the correct line in the source-mapped file even tho the console link gave the correct line).
One thing I miss that Firefox does not have at all is the Layers view. Which would be especially important since such things are browser specific and debugging performance/memory issues and making sure the engine uses a sane set of compositing layers can be important sometimes.
But the feature I miss most in my tiny corner of the world by a large margin is the Websocket support indeed. This is the thing that always makes me go back to Chrome devtools.
However, to be fair, this is a strong sign that as a developer, we are doing something wrong. If a JS application feels slow on an average browser in an average computer, it will feel slow on all slower computers. The usability will be crap. In this particular example, the frameworks are not suitable for such a large number of "reactive" elements.
And yes, I too have wondered if they only test in Chrome.
That's not me saying Firefox's tools are actually better though, there's still a number of weird quirks or features that could be lacking, while also having features I can't find in chrome that I also take for granted
Chromium for web dev.