As squirmish as this makes me, this is exactly the kind of thing that the original architects of the web imagined when they describe the browser as a "user agent" - that the browser doesn't have to show you exactly what the server sent you.

The user's agent is free to transform the data sent by the server in any way, and users will seek out agents that do useful things for them.

As a developer I'm uncomfortable with the idea that some browser or extension might break my site, or that I may break the customization with an update, but the idea here is really powerful. I don't think it's ever caught on much though. I think most extensions that do this kind of thing have pretty solidly failed.

Yes, but usually the “user” in “user agent” refers to the person using the browser, not the advertising company that controls it.

It's certainly a powerful idea, but I wonder how well it translates to users that don't even know what a browser is, let alone understand what it means for that to be "acting as their agent".

AI has got people thinking about this again. I'm hopeful that there will be at least some browser features that will genuinely act on the users behalf in a largely adversarial online information environment.

If the original architects of the web didn't foresee corporations owning the browser so they can inject ads and propaganda into a publisher's content, of what use was the vision?

> user agent

With user-defined CSS style sheet?