Back in September, we announced that HTTPS support was coming to blogspot.com, making it possible for you to encrypt connections to your blog; since then, many of you have enabled HTTPS for your blogs. In some cases, not all of your blog’s functionality has worked over HTTPS due to mixed content errors often stemming from your template, gadgets, or blog post content.
To help spot and fix some of these errors, we're releasing a mixed content warning tool that alerts you to possible mixed content issues in your posts, and gives you the option to fix them automatically before saving.
To use the tool, turn on HTTPS for your blog, open the Blogger editor HTML view, and click Save or Publish. If the editor detects any errors they will be shown above the editor, along with the option to fix the errors found.
Posted by Shweta Karwa, Software Engineer, Security.