The main reason we can't easily use hashes to bust the cache is that the includes for our static assets (the Firebase JS lib) are happening inside our customer'

The main reason we can't easily use hashes to bust the cache is that the includes for our static assets (the Firebase JS lib) are happening inside our customer's websites. We could hypothetically insert a shim that pulls the include down the hash appended resource, but could still have the same problem with the shim itself. The custom origin has alleviated many of our pains but wouldn't have taken us all the way. As people have begun to use Firebase to power Facebook apps (mandatory SSL for the canvas) and other SSL only environments, we needed the CDN to support it. We had a stop gap for some of our user (using Amazon's domains) but it would've added too much friction in the docs to explain the domain swaps for justify keeping this hack in place.