This permission is harmless because native messaging only allows an extension to communicate with a specific native companion program that has to be installed/enabled outside if firefox.

If you don't install the companion program, this permission won't do anything.

It does not allow the extension to run arbitrary programs.

Where and how is this program specified? Can malware impersonate itself as a "companion program" and collect user activity data?

It's just specified in a manifest file in a specific location on Linux or referenced in a registry key on windows, so sure, if you already have malware running on your computer I suppose it could do that (assuming the messages sent by the extension contain browsing data) but there would probably be easier ways for it to collect your data.

The permission request should probably be reworded to make that more clear.

Bookmark access for the container extension is optional and there is a toggle button for it; for some reason, this one was added to the "Required permissions for core functionality" list which can not be modified.

> for some reason

I think these permissions cannot be optional: https://extensionworkshop.com/documentation/develop/request-...

(Not sure though, I haven't worked with optional permissions for my extensions yet.)

I'm not sure if it's possible for this permission yet, but it did become possible for extensions to dynamically requests access to page contents per site, rather than declaring them all up front. It requires the extension authors to use a different API though, which not everyone has switched to yet.

I was thinking the same thing when I was reading this link too.

Another thing I'd like is for Mozilla to not be able to deactivate extensions remotely.