An exception for http sites is also available for chrome users.
To apply it a user needs to go to the site in question (needing to press the "continue to site" button on the warning screen that the site is not https).
On getting there to the left of the web address is a button which will say "not secure". Click on that, and then Site settings.
Scroll down the permissions list to "insecure content" and change from "block" to "allow", and the browser will remember this preference for this site only.