http - Is there any downside for using a leading double slash to inherit the protocol in a URL? i.e. src="//domain.com"

Question

I have a stylesheet that loads images from an external domain and I need it to load from https:// from secure order pages and http:// from other pages, based on the current URL. I found that starting the URL with a double slash inherits the current protocol. Do all browsers support this technique?

html ex:

<img src="//cdn.domain.com/logo.png" />

css ex:

.class { background: url(//cdn.domain.com/logo.png); }

Answer 1

If the browser supports RFC 1808 Section 4, RFC 2396 Section 5.2, or RFC 3986 Section 5.2, then it will indeed use the page URL's scheme for references that begin with "//".