Brown Fat - Keeps You Warm And Keeps You Slim

No it doesn't keep you slim - at least these researchers have not proven that it does.

People with more brown fat seem better able to stay warm when it is cold, Canadian researchers reported in the Journal of Clinical Investigation. They added that the findings of their study could eventually be used to find ways of fighting obesity. Not much has been known about brown fat, a type of good fat, until recently...

Experts say much remains to be known regarding brown fat, but the main differences between these two types appear to be:
Brown fat burns through calories in order to generate heat
White fat is a storage area for excess calories

Which means that as long as people consume more Calories than they burn, they will accumulate fat.

Period.