This gives a lie to the identity being an "email address". It isn't. Ok, it's structured as a LHS@RHS form but the domain in the RHS isn't an email domain, it's an overloaded website with some problematic assumptions ladled in.
This creates a significant barrier to adoption. Many entities just won't bother: not only does it ask an apex A record to serve actual content (usually a mistake) but it requires the primary web host of a registerable domain, usually a trademark or brand identity, to carry technical material, definitely a clash of concerns.
(Why? In many companies of reasonable size, the website is managed by a completely different group of people - often a marketing team - to the internal identity service. Then, even if one team convinces to the other to install the browserid file, there is a possibility of it being deleted it by mistake during the next site refresh.)
I had hoped to find an intermediate step where a DNS SRV lookup was used to first locate the host delivering the browserid file. This follows the federated structure of email rather more closely and allows the identity service to be independent of the corporate brochureware. Even better - if the SRV lookup could be signed with DNSSEC, the transfer itself can be protected with DANE. The whole thing becomes manageable as a simple, separate unit of technology. It is thus rather more likely to gain the support of system administrators.