Quotes from the blog post:

We’re taking a steady approach to opening up the mobile extension ecosystem to ensure Firefox for Android maintains strong performance standards while a vast new array of extensions are utilized for the first time in a mobile environment. If testing continues to progress well, we anticipate unveiling a fully open Firefox for Android extension ecosystem sometime in December.

We anticipate strong interest from users excited to explore all the new ways they can customize Firefox for Android. Current trends indicate we’ll have at least 200+ new Firefox for Android extensions on AMO when open availability debuts in December. And while a couple hundred extensions is more variety than you’ll find on any other mobile browser, it is significantly fewer than the nearly 40,000 desktop Firefox extensions on AMO. So the opportunity for heightened discoverability with new users may be intriguing to some developers.