The favicons for Area 51 and Stack Exchange that are shown on sites marked "beta" in the Site Stats widget are using
http:// URLs for favicons when visiting the sites over HTTPS.
Mixed Content: The page at '...' was loaded over HTTPS, but requested an insecure image '...'. This content should also be served over HTTPS.
These are the links requested:
- (redirects): http://sstatic.net/area51/img/favicon.ico
- (redirects): http://sstatic.net/stackexchange/img/favicon.ico
They should be using something protocol-agnostic.