Mora I have experienced the same.
It is OK to follow the existng steps for setting a permanent exception.
Once enabled (or disabled) this setting could remain for all pages with the same domain (eg. all subdomain.domain or domain/allfolders) as long as the browser is not closed, or the setting is not toggled back.
If the user closes the browser and then revisits the same page, it would have reverted to its default setting.