I believe you.

I also do not, and have never, experienced this. I've been using Pixel phones since the 3a in 2019/2020.

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.

Sorry, forgot to say pixel 7a, not sure why I got downvoted though?

I'm still going to use Firefox, I just hope the battery issue I experience goes away.