That's surely not clear from the blog post. I just read it again and I still can't find it; indeed, the only links to apps are links to the existing Firefox Pre

That's surely not clear from the blog post. I just read it again and I still can't find it; indeed, the only links to apps are links to the existing Firefox Preview (not even to Firefox Nightly, which is what the article seems to be talking about). Searching the store turns up both "Firefox Preview Nightly for Developers" and "Firefox Nightly for Developers" which is consistent with your claim but is not necessary supportive of it. The title refers to an app apparently called "Firefox for Android Nightly" but no such app exists that I can find in the store. It is possible this is one of the worst public announcements ever. A link to the product they're announcing to would have made a significant difference.