From what I could understand :- Bridge tables are used when a dimension table can not be directly associated with a fact table.
e.g. In a bank's data warehouse a fact table of balance of a customer can't be stored with a customer ID as link between fact table and customer dimension due to the fact that multiple customers can be associated with same bank account. (i.e. joint account)
So fact table store account ID and bridge table between account dimension and customer dimension is used to distinguish.
But how are they different from helper tables which resolve many to many relationships between fact table and another dimension?