I'm not sure when this started happening, but I noticed today in Google Chrome (and subsequently in Firefox & IE) that my Joomla 3.9.20 site is causing a "Mixed content" warning. I searched the .html source for instances of http://, and there are none.

Using Google Chrome's developer tools network tab with the filter mixed-content:displayed, I see two requests, in the name column it says www.my-site.com (well, it says my actual site's name), in the status column it says 302, in type it says "text/html", in the Initiator column it shows the path to two .png images (existing_image_thumb.png) (i.e., it seems to be trying to get _thumb version of two existing images). I don't understand this. How can a .png image initiate a request for the main page?

I did notice that some other images displayed on the home page that are not causing this error have a _thumb file in the same folder as the 'normal' image, but the two images causing the issue don't have that _thumb file. Could this be the issue? How are those _thumb files generated anyway? The site uses a RocketTheme template, perhaps the _thumb file comes from the template?

How do I diagnose, and fix, these mixed content warnings?

1 Answer 1


Yes, it turned out the missing _thumb files were the issue. I just copied the original image file with a _thumb extension, and that resolved the issue.

Also, in my .htaccess file, there were some entries like:

ErrorDocument 400 http://www.my-site.com

I modified those to be https://www.my-site.com instead of http, and that resolved the mix content issues when there are missing images.

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