Updating a products firmware and having it fail in the process is a product failure under normal use and maintenance. The customer has a right to return a product if a product failed under normal operation for which the product was designed.
Retailers and business which do not honer returns for these reasons are rather short sighted as the consequences they themselves are creating and the potential return and referral business they are losing.
Now if you use a product in a manner other then its designed use and it fails then that's a different scenario where a return could be reasonably denied. (Using a passenger elevator to move around fright, using a rubber mallet to break up concrete, using an indoor security camera outdoors, modifying equipment in a manner other then for which it was designed, are some examples where you did not use the product under its designated operating conditions or intended purposes / applications)
If a Manufacturer creates a product which fails under use for which it was designed for then they should accept the return. Large volume retailers have contracts that stipulate terms of returns and acceptance of faulty products and goodwill returns. The retailer creates for itself return business and a satisfied customer and the manufacturer absorbs the cost of replacing a defective product and takes it as a cost of doing business (a business expense).