«While we still use it heavily, IRC is an ongoing source of abuse and harassment for many of our colleagues and getting connected to this now-obscure forum is an unnecessary technical barrier for anyone finding their way to Mozilla via the web. Available interfaces really haven’t kept up with modern expectations, spambots and harassment are endemic to the platform, and in light of that it’s no coincidence that people trying to get in touch with us from inside schools, colleges or corporate networks are finding that often as not IRC traffic isn’t allowed past institutional firewalls at all.»
Oh, I thought you just needed a source on the harassment claims. I do not believe there was an explicit rejection, however at the bottom of the blog post, we have...
* We are not rolling our own. Whether we host it ourselves or pay for a service, we’re getting something off the shelf that best meets our needs.
* We are evaluating products, not protocols.
* We aren’t picking an outlier; whatever stack we choose needs to be a modern, proven service that seems to have a solid provenance and a good life ahead of it. We’re not moving from one idiosyncratic outlier stack to another idiosyncratic outlier stack.
Given other language such as "modern expectations" in regard to interfaces and being "spoiled for good options" as well as Rust's move to Discord possibly setting a precedent within Mozilla, the posters in the HN thread above don't have a lot of hope Matrix will be selected even via Riot.
https://news.ycombinator.com/item?id=19763276
http://exple.tive.org/blarg/2019/04/26/synchronous-text/