Persistant permissions over HTTPS for GUM is a behavior 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 security prompt, this is by design for the sake of security. What we can suggest is to use one of our branded/commercial plugin. With the branded version, a list of domains are provided and they are added to the whitelist. The plugin will then solely work only on those domains. This will result in no popups where users would be prompted to grant permission to the mic/camera