Absolutely.
Although the market for centralized secure messaging is currently being served adequately by the likes of Signal and Telegram, centralized messaging platforms inevitably leak metadata.
I don't want to belittle the work done by teams that have already started work on distributed messaging platforms like Tox and Matrix (and my own proof-of-concept, Toc [1]), but Mozilla is in a much better position to tackle the problem of decentralized, private messaging that also has great UX, and not just in terms of sheer resources:
1) They have (or at least had) a decentralized identity management platform in Persona.
2) They have a decentralized, zero-knowledge data sync platform in Firefox Sync.
3) They have a lot of influence in the web standards community that they can leverage to push a new federated messaging protocol to succeed XMPP.
This is the kind of work that I think Mozilla should be doing, because they can do it better than anyone else who's willing (i.e. not for-profit corporations, because they have very little to gain by building decentralized apps and federated protocols that have no lock-in whatsoever).
[1] http://toc.im/