"Do you want to view the webpage content that was delivered securely...."
Is this message displayed only because http resources are used in a https resource?
"Do you want to view the webpage content that was delivered securely...."
Is this message displayed only because http resources are used in a https resource?
Yes. Usually this is static content, such as image, CSS, and JS files.
It is best to avoid mixing content sources on HTTPS pages, as it will cause these sorts of warnings, and can lead to some of your content not displaying to the end-user.
As you said in your question, it's because of the mixing of both http and https content.
If you are using Firefox you could go and install the Firebug addon to look up all resources that are loaded and then use only one source. You'll find all loaded content under tab 'Net' after you do a reload.
That's correct. It's unsecure to request HTTP resources from a HTTPS page. You need to replace all absolute URLs to resources by scheme relative URLs.
E.g.
<link rel="stylesheet" href="http://example.com/resources/style.css" />
<script src="http://example.com/resources/script.js"></script>
<img src="http://example.com/resources/image.png" />
must be
<link rel="stylesheet" href="//example.com/resources/style.css" />
<script src="//example.com/resources/script.js"></script>
<img src="//example.com/resources/image.png" />