The interview article is mainly for addon developers, this is the reason of the answer for the question. In past days I was a "people pleaser" and I didn't say "no" from my frailty, then my old addon became too fat, and finally dead. I hope that addon authors publish long-living small addons instead of short-live too much addons.
The sentence in the interview means that now there is a boundary of responsibility between addon and Firefox. If a feature request is impossible to be implemented due to API restrictions, it have to be solved by Firefox itself. Thus if I have strong motivation to implement a new feature requiring new API, I still file a proposal of new API, and I think other addon authors also should do it based on his demand.
There are two reasons, the first is there. The second reason is my job. I'm employed as a support engineer for company-use of Firefox/Thunderbird for 11-12 years, and the knowledge and trust are based on my addon development experience. So, I think I already monetized from addons and donation looks like a double-dealing for me now. (So after I retired I may accept donation, if Firefox and my addons still alive.) Anyway, I just say thanks to all!
As I wrote in the article, indeed I worried about death of addons in last 2 years. But, from various viewpoints I analyzed Mozilla's statements around addons, and finally I decided to forget past and shift my mind moving toward to make things better. So the story of the interview is almost correct.
The sentence in the interview means that now there is a boundary of responsibility between addon and Firefox. If a feature request is impossible to be implemented due to API restrictions, it have to be solved by Firefox itself. Thus if I have strong motivation to implement a new feature requiring new API, I still file a proposal of new API, and I think other addon authors also should do it based on his demand.