Yeah, the article's quoting didn't help its case. It doesn't seem fair to quote someone saying [I don't think X is a good idea] as evidence they are about to do X.
That being said, in the original context [0] it does sound a lot more like an option on the table. That original article presents it as the weakest of a list of things they're about to explore - but who knows, maybe the journalist has butchered what was said. It is an ambiguous idea without more context about how close it is to Mozilla trying to make life hard for ad-blockers.
[0] https://www.theverge.com/tech/845216/mozilla-ceo-anthony-enz...
The part about making money through advertising and selling data to 3rd parties (though "search and AI placement deals") is already not a good sign. Planning to make their money through ads and surveillance capitalism is already making it impossible to say "I always know my data is in my control. I can turn the thing off, and they’re not going to do anything sketchy"
It might just as well have been something that was supposed to sound young and fun ("I don't want to do that") and ends up leaving too much room for interpretation.
If you have the power to do something, saying you might do it but that you don't want to makes people imagine you'd do it. If you have a knife and talk about how you "might stab people, but don't want to", that's a very different message than having a knife and saying "obviously I'm not going to stab people, violence is not an option".
The latter reassures, the former depends heavily on what the recipient of the message thinks of you, and whether they can imagine you stabbing people.
If that quote was accurate, then either he just said something and wanted to wing it, or they should reconsider their communication strategists.
Except that expressing loud doubts about something ethically dubious is often a sign that an opposite action will be taken. So many business people want this moral excuse "but I had doubts" while being totally cynical
In addition "off-mission" is a pretty weak way to describe completely destroying your credibility and betraying your user base. Building the Firefox phone was off mission. Buying Pocket was off mission. Maybe it's just me, but selling your remaining faithful users down the river to make a quick buck from advertisers seems a little, I don't know... worse than that?