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.
Firefox on Android 16, it sucks the battery up in background mode (even with permission to use background turned off).
If I manually close it no issue.
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).