The full answer for this is a long, wild ride which would fill entire chapters... but the short answer is: Zen's author broke the extension API so badly it's literally impossible to do a lot of what my extension needs to do... and the author is aggressively opposed to fixing it or even admitting that he broke it.

More generally, Zen Browser is the buggiest browser I've ever encountered... by a wide margin. Some of the issues are jaw-dropping. It's notorious for losing user data. And looking at its history, it has mostly just kept getting worse over time. Extensions which used to work don't any more, because he keeps breaking more and more stuff.

I tried to support it. But instead, I got a quick education on why nothing supports Zen Browser. They can't... because of the guy behind it. Sometimes due to his incompetence, sometimes because he actively intervenes when people try to support it.

So... my experience with Zen Browser rapidly went from "hey this seems neat" to "wouldn't touch this with a ten meter pole".