Hazel doesn't close tabs because it's 'like a trip down memory lane.' Mozilla says it has some profile and tab group features coming later this year that might help her organize those memories.
God, I think I had 500 open on my old phone alone... Though I usually don't pass 50 on desktop, because they're easier to manage and harder to bury or forget about
I have like 20 on my phone, usually 100-200 on my desktop, so the reverse. Since tabs are harder to manage on my phone, I tend to clean them up a lot more often.