My issue with stable is that it's slow. Everything about it is slow. Pages that load immediately in Chrome take double digit seconds in Firefox. When they do load, scrolling lags my finger and jerks around, and zooming is noticeable unresponsive. The acceleration curves feel off too. On my mid-range tablet performance is so bad it gives me a headache.
So I might open a link in my email app, then when I tap the back button on the phone, the expected behaviour is it will close the tab and return to the email app. Instead I'm finding it navigating back to the page that was open previously on the tab that was already open.
On heavier sites it's inevitable that it will crash. Years ago Chrome/Chrome Beta also had this problem (the root cause is with the phone hardware/android) but somehow they managed to catch it and not bring down the whole browser app.
I still use it despite the other main drawback (being slower than chrome beta on heavy sites, like say twitter) because I like my uBlock and tab-sync, but every so often I get so annoyed at it that I avoid it for about a month until Chrome even with basic adblocking via Blokada makes me mad enough to switch back.