What does this Https field represent without a lock symbol?

There is mixed content on that page.
Firefox only blocks active mixed content and if other mixed content like images are present then you still get the globe instead of the padlock.
You can see that in the Web Console (Firefox/Tools > Web Developer;Ctrl+Shift+K) as red lines.

Thanks Cor-el

I understand that content is mixed. Is it possible to prevent any non https from being displayed or accepted? Because https has no meaning if a user cannot determine which content is secure.

See:

• https://developer.mozilla.org/en/Security/MixedContent

There are these two pref that determine what content is blocked or passed

• security.mixed_content.block_active_content (true)
• security.mixed_content.block_display_content (false)