Persistent permissions over HTTPS for GUM is a behaviour found in browsers where the permissions grant for media device access is retained for a domain accessed via HTTPS for future sessions. This is not yet available in any currently shipping version of the plugin.
The free plugin does not offer any facility to disable the prompt. This is by design for the sake of security.
We would suggest using our commercial plugin, one of whose features is the absence of the "Select input device" prompt. Basically, when using our commercial plugins, a list of domains are provided and added to the whitelist. The plugin will then solely work only on those domains and all getUserMedia requests made on whitelisted websites will automatically be approved, without the user needing to validate them, resulting in no popups where users are prompted to grant permission to access the mic/camera.
This feature is not available with our Free Plugin. You can read more about our plugin pricing and features here. To discuss commercial plugins further, please contact our Sales Team at firstname.lastname@example.org.