Edge/Internet Explorer: “This page contains both secure and non-secure items. Do you want to display the non-secure items?”
Chrome: “This page contains other resources which are not secure. These resources can be viewed by others while in transit, and can be modified by an attacker to change the look of the page.”
Firefox: Users will not receive an error, the browser will just show a red line through the padlock.
Safari: Users will not receive an error, a Yellow Padlock icon will appear when the address bar is clicked.
Resolving Insecure Content
This isn’t a difficult problem to solve, just replace any http:// references with secure ones so they loaded through https://. If content can’t be loaded securely, you shouldn’t be loading it, lest you continue to get security warnings.