I agree Gavin, it would be great to have it supported as long as possible.
Having that said, the notice is shown by our system simply to let you know of browser specific requirements.
For example, screen recording works nicely with Firefox without any plugins. However Firefox requires the screen recording to be done over HTTPS pages.
On the other hand, WebKit based browsers require standard recordings to be done on HTTPS pages, as well as the screen recording.
This is what this notice is about and it should allow you to use your localhost and work properly.
The idea was to let all of the developers know of these requirements by browser vendors so that they have time to add HTTPS on their website before they implement any powerful features.
For example geolocation and video recording are just some of the features that are impacted by this.
Here are the references that show you more on this subject: