In the coming months Mozilla will launch support for an open ecosystem of extensions on Firefox for Android on addons.mozilla.org (AMO). We’ll announce a definite ...
They are, since there are definitely benefits and makes migration easier, but they are also allowing the support needed for adblockers to be just as strong as they are now. So it keeps the benefits while also keeping adblockers strong like right now.
The issue is that Chrome is trying to replace webRequest.BlockingResponse which is essential for content blockers, which Mozilla is pointing out and keeping supported.