The gray triangle with ! in it indicates that the connection to the site is secure, but some content in the page was not retrieved over a secure connection. The content is still displayed because it is not considered highly dangerous -- for example, it could be some photos that were embedded from a site using HTTP instead of HTTPS. This mixed display content warnings differs from the mixed active content block, for which you see a "shield" icon in the address bar, and if you approve it, an orange triangle.

Sometimes Firefox will give a "false" mixed display content warning on some sites when you use the Back button. This seems to be an issue with cached files. To bypass the cache, you can reload the page fresh from the server using Ctrl+Shift+r (instead of a regular reload). If you find that this is your problem, there may be a workaround (modifying how Firefox caches pages).

If that is not the problem, do you want to give the URL of a page that shows completely secure in other browsers but gives a mixed content warning in Firefox? This might not work for pages like the FB news feed which are different for everyone...

If there is mixed passive content (e.g. images) then Firefox shows an exclamation mark instead of "Site Identity Button" (globe/padlock) on the location/address bar.

• https://developer.mozilla.org/Security/MixedContent
• https://support.mozilla.org/kb/how-does-content-isnt-secure-affect-my-safety

See also:

• https://developer.mozilla.org/Tools/Web_Console