I'm using the latest version of Firefox on the latest version of OS X for reference. I've noticed that sometimes when I go back to my email tab and look in the location bar, Firefox says gmail is no longer encrypted. Clicking on the icon on the left of the bar says the same and that the connection may be eavesdropped on. I have HTTPS always on but this still happens. My questions are:
Why is this happening and can I stop it?
Can others on my network see the contents of my email?