I noticed the same thing. It seems like there’s a lot of background battery usage. I switched it from “optimized” or “unrestricted”, I don’t remember which, to “restricted”. I don’t use Firefox for any reason I’d want notifications, so I don’t need it running in the background at all.

The one downside is that I have the search widget on my phone set to open things up in a private window, which is nice to avoid ending up with 1000 tabs open, but private windows now are not as persistent. Like if I looked up a recipe in a private window, a few minutes later, that window will be gone. I might have to switch the power setting to “optimized” and find a way to reduce background battery usage from within the app