Something I didn’t consider when answering earlier is that even if Firefox did have good RAM usage limiting built-in I probably still wouldn’t use it or recommend it, because one of Firefox’s biggest problems is that it leaks. And memory leaks will not be negated by Firefox’s built-in RAM limiter but they will be by systemd’s (or anything else you might be using instead) Firefox would still crash in the event of a leak but it’s still better than it taking gnome or other apps with it, or freezing your system entirely.
I don’t know how it is on mbin but on Lemmy the best thing to do is message the admins directly, and not bother reporting. This is because Lemmy’s developers give way to much credit to the legitimacy of forum moderators and do not allow a way for reports to only be sent to administrators, meaning that community mods like these can easily dismiss reports before they are seen by admins. So best thing to do is message them directly at the current time.