I'm sorry, but that still doesn't answer my question of "is it secure (enough) or not". It's actually the reason why I decided to post this question here, as I was hoping to get some counter-arguments to that.
It depends on whether you're especially likely to be targeted, whether you're running on a phone with a lot of private information or whether you're using a burner phone where you don't lose a lot if it gets compromised, whether you expose yourself to malicious content, etc. etc.
As you said you regularly visit "shady" and "weird" sites on what would presumably be your personal phone, and as I presume there is definitely some information on your phone you wouldn't want others to have, and especially since someone with control of your phone could take over any accounts that use your phone as a 2FA source, I would say that no, Firefox is not secure enough.