They have a knowledgebase article explaining why …

… that doesn’t explain why. Yes it explains the technical mechanism by which extensions can be blocked, but no explanation why this feature is even there. There’s just a sentence about “various reasons, including security considerations.”

I think it would help if they explained some of those “various reasons”, maybe with an example. Then I might even agree that those are situations where that might improve the user experience. Or the security.

But I would absolutely demand a transparent process for how, why and by who these decisions get made. And possibly a way to enable the extension regardless - you open a page, an extension is blocked, you get a notification explaining why and giving you an override option.

Part of me wants to believe that this is just very poorly communicated. Mozilla has been doing this for a while, for example extensions don’t work on addons.mozilla.org or any of the about: pages. And that seems reasonable to me. But I also don’t like the thought of mozilla policing what a user is or isn’t allowed to do.