Reduce users' fingerprintability

Feature Request

There are some things websites could use to get some bits of information to identify users with an extension which runs a content script on the site:

• The script uses postMessage to stop an old version of itself. A website could listen for message events and detect differences between users.

  postMessage could be substituted with a custom window event whose name includes a unique string (such as the ID of the extension). Then the website would at least need to check for the specific extension separately rather than just passively listening for message events.

  Additionally, it would be nice if it was possible to disable that functionality entirely in the case of it being unnecessary for certain scripts.

• Content scripts injected to the MAIN world add a property to the window object. A website could e.g. hash the keys of window and get different values for users with an otherwise identical browser depending on whether they have an extension installed.

  defineUnlistedScript could perhaps wrap its result in an IIFE. injectScript does not seem to return the script's return value anyway, so another way to communicate is needed if that is desired. For executeScript, the IIFE can just return a value rather than setting a global.

• A MAIN world content script which does nothing else to make the web page aware of its existence but throws an uncaught exception will cause console.error to be called, which a site could detect.

  This one probably doesn't warrant changes in the code as a developer concerned about that can just wrap their main in a try-catch.

Is your feature request related to a bug?

N/A

What are the alternatives?

Leaving everything as-is.

Additional context

N/A

Start by tracing the content-script handling behind postMessage and the MAIN-world entry points defineUnlistedScript, injectScript, and executeScript. Review how each currently exposes extension presence, then clarify which fingerprinting reductions are in scope. Done means the selected behavior is implemented without unnecessary page-visible signals and its communication behavior is documented or covered by the project’s existing checks.