I have the following favicon loading via header.php:
<link rel="shortcut icon" type="image/x-icon" href="<?php echo esc_url( home_url( '/wp-content/themes/themename/img/favicon.ico' ) ); ?>">
My site has an SSL certificate installed. Google Chrome loads the each page over SSL perfectly, but Firefox flags a mixed content warning. I can see via the source (both in Chrome and Firefox), that the favicon is being served via http.
I can't work out why this is happening.