That preference is a simple on or off. Unfortunately, there is no way to whitelist specific add-ons or websites using this preference.

Sorry.

Is there any plan to implement this feature?

I don't believe so.

The people who answer questions here, for the most part, are other Firefox users volunteering their time (like me), not Mozilla employees or Firefox developers.

If you want to leave feedback for Firefox developers, you can go to the Firefox Help menu and select Submit Feedback... or use this link. Your feedback gets collected by a team of people who read it and gather data about the most common issues.