I also use Firefox on Android, I have less experience of using other browsers on mobile but what I've got is fine for me.
I'm not questioning your experience but I would like others, who might be considering using Firefox, to know that different people have different experiences.
For what it's worth, I've been known to have 300+ tabs open all in separate windows (I just forget about them and they tend to accumulate), and for the most part it handled it just fine (it did use quite a lot of RAM, of course.) That was on an i7 7700k with 32GB of RAM.
I remember being quite impressed indeed.
A few hundred HN or Wikipedia tabs work absolutely fine, I've tested. But there are much heavier sites, and only a few of those can cause the machine to start swapping until OOM, especially when left to work in the background.
(And unlike Chrome, Firefox does not seem to throttle/unload background tabs automatically... or if it does, it does it much less aggressively)