The ability to prevent an extension from accessing specific sites is an improvement as long as the user can control it and it is not used for centralized access control.

The reason this feature is there is that many extensions play poorly with or should not have access at all to specific sites. For example, Grammarly has no business accessing a corporate billing system and IT might want to disable access. In other cases an extension slows a site massively and a user might want to say, "not that site" to an extension. This could be the start of a big end-user improvement, especially if it can be managed by users and installers.

This as a feature attached to their containers would be pretty spiffy tbh. But as you said, if it was entirely user-controlled.

If that was the case, the feature should have been moved to site settings and labelled "Disable extensions on this site" or even better "Allow only specific extensions to run on this site".

> why exactly is there to begin with is the real question

And "it's confidential" is the worst possible answer but it's still the one they gave us.

The commentor you've replied to says:

> The best faith interpretation I can come up with, is in fact for security purposes. It creates restrictions on (at least from Mozilla’s perspective) untrusted extensions. I mean how many extensions are there that do act maliciously? It probably isn’t trivial.

My best interpretation of that is it allows organizations to more easily allow some extensions while disallowing others.

Firefox is lagging behind on enterprise configuration options. Adding in additional features that allow sysadmins to deploy policies that can further control Firefox like Chrome and Edge could be potentially behind why this is happening.

This is of course, complete speculation and if it was for enterprise management reasons, Mozilla should have clearly communicated it.