I think this is an excellent example of such an unobtrusive prompt and is how ALL such features should be implemented. Sites should get almost no permissions by default and certainly not be able to show popup prompts.
When the site tells them to "active X permission" without telling them how to (for their specific browser version), most will leave instead.
When the site gives super detailed, up-to-date instructions on how to activate the feature, a very large percentage of users will still leave instead.
When the feature is so useful that many sites go through all thouse troubles and it's common enough for users to encounter this that they'll follow through, most will do so for every site that tells them to and entices them with "ACTIVATE X TO RECEIVE YOUR $10,000 PRIZE, LUCKY WINNER!!!".
network.trr.mode I'm looking at you.