One thing to keep in mind is thar mozilla is now an ad company and can use this data itself for whatever advertising it wants to sell, so they dont even need a third party they can just sell targeted ads directly to companies while not technically "sharing" the info they gather to anyone.
Basically, why sell the data to other people when you can profit from using it directly?
You cant use it with grapheneOS, ive tried. I mainly use bitwarden for passkeys but some (most?) services only work with googles version