Secured site with insecure content
Summary:
Matt's answer:
The answer is no, at least not for Google. Google doesn’t really differentiate and say, oh, you had a secure or SSL version of a page, and then you included insecure content.
That’s not a ranking factor right now.
But I would recommend that you look into making sure that all of your content works, just for your user’s sake. Because whenever a user’s browsing, different browsers will do different things. Internet Explorer might pop up a warning. Chrome might have a little x through it that’s red. And sometimes, that can make people a little more stressed, even if it’s something that’s relatively safe.
In fact, Chrome has just recently started to make it so that if there’s an insecure script, it will not load it by default, and you’ll actually have to say, OK, load this script anyway.
There’s no reason to worry about mixed content.
But for the user experience and just making sure that things are clean in general, it would really be great if you can offer unified content that’s all in HTTPS and not have mixed content on HTTP and HTTPS if you can help it.
by Matt Cutts - Google's Head of Search Quality Team