From MozillaWiki

Here's a summary of what we got right and what we could have done better with Persona, distilled from a lot of different conversations with people inside and outside of the core team.

What did Persona get right?

We built a simple solution that developers love.

Users and developers trust Mozilla and want us to fix identity on the web.

The demand for "solving the password problem" is increasing with every high-profile password leak and advances in password-cracking tech.

As the 2013 Snowden relevations have shown, decentralized and privacy-respecting technologies are badly needed.

Why did Persona fail to gain wide adoption?

We were in a three-way cold-start between users, providers, and websites. More info on Hacker News.

We started building a whole identity stack but it's really hard to do things in a decentralized way.

We experimented outside of Firefox and could not leverage the Fx user base or Mozilla's marketing / evangelism resources.

We offered an easy and secure solution but large sites that have enough resources to allocate to their login experience don't care.

We made Persona a user-visible brand but that competed with a site's own brand.

We looked at Facebook Connect as our main competitor, but we can't offer the same incentives (access to user data).

We built complex features (session management) that our users did not want, and which made Persona difficult to use or understand.

What did we learn?