One of these banners? http://www.missingkids.com/banners Unfortunately, it appears that they only support HTTP connections, so if you are trying to embed it into an HTTPS site, it will create a mixed content situation. The end user documentation on that is here: [[How does content that isn't secure affect my safety?]]

I am not sure it is Firefox stopping you from modifying your own website. Firefox may be trying to prevent you using something that is unsafe. When I try * https://www.missingkids.com/ I do get warning the site is not trusted * [[How do I tell if my connection to a website is secure?]] *'''[["This Connection is Untrusted" error message appears - What to do]]''' * This independent test site confirms there is a problem <br /> https://www.ssllabs.com/ssltest/analyze.html?d=missingkids.com&latest You may want to contact the site * http://www.missingkids.com/home Make sure they are aware of the problem. I have not tried to check the banner, but I would not rule out that there is a possibility, putting a banner from such a site on your own site could have a detrimental effect on your own site.