Our live demo project (for example: https://demopublic.magnolia-cms.com/.rest/delivery/tours/v1/magnolia-travels/A-Taste-of-Malaysia)

Does not render properly in some browsers, such as Firefox. Possibly because it appears to miss the content type header.

It should render properly in Firefox, and it should include that content-type header. 

You can see how it should be rendered (and used to be rendered) in our Getting Started documentation. See the "REST result" column:

https://documentation.magnolia-cms.com/display/DOCS57/Getting+started+with+REST

Note:

On November 18, 2019 6.2 snapshot CE demo bundle running locally on HTTP I do see the contenttype header, and it does render properly in Firefox.

So I think the problem may be just with configuration of demopublic server. (CORS or content security issue?)

This is important because "Headless" usage of magnolia is increasing and checking out our public demo is part of the evaluation path. The current display is un-professional and will discourage an evaluator.