Questions about HTTPS

So, it’s highly advised that you use HTTPS connections when you’re login-in, or sending private info, like when shopping online. So I got a few questions.

  1. if a page is HTTP but has embedded login form, kinda like this forum (screenshot 1 upper-right corner) is there a way to know if that login form is actually secure?

  2. Sometimes you get mixed padlock, saying something like "This page is secured, but contains unsecured content’ is there a (relatively) easy way to tell what elements of a page are secure, and what aren’t? Maybe some kind of extension?

  3. Why the login page for this forum (appears to be) unsecured (screenshot 2)?

  4. Would you recommend using such extensions as HTTPS everywhere? Maybe there’s a better one?

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I always use the function shown in the screenshot. (Dragon is my browser).

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