You know I let a lot of important things in Firefox slide (like the poor Webspeech API support, bad text-to-speech, some missing extensions and a lot of other things) but I still make it a habit to use it over Chrome (and recommend it to everybody) as somewhere in my mind it feels like a small revolt against the giant evil Google corp.

But stuff like this and other shenanigans in the past (like Mr.robot, misuse of funding, etc) is really off-putting sometimes. It really makes me feel naive and just drinking the support open-source kool-aid.

I switched to Brave - no regrets

I did, too. All I can tell you is that when I have Brave running on an M1 with four tabs open, it's consistently using 240MB of memory. When I fire up Firefox Developer Edition with the same tabs open, it starts at 660MB and quickly balloons up to 1.05GB of memory usage.

How are the devtools in Brave?

They're comparable to Chromium's, if not identical: https://github.com/brave/brave-browser