I've used Firefox across devices, across the years. This just isn't my experience, at all, remotely. And I have had to use Chrome (now it is Edge) for many work functions, so I do have the A/B comparisons. I'm not doubting your experience, fine, but I also know I'm not "pretending" anything in my own experience.
doesn't happen in my case (OnePlus 15/Android 16, Firefox background usage allowed in some "smart" mode whatever that means, doesn't suck the battery in background although it's on most of the time).
I have better battery life on Furi FX1s than any of my Android devices (Pixel 6a, Fairphone 4). This is with closing applications when I no longer need them on all devices.