On Youtube, the connection is encrypted (green padlock). However I found myself in a situation that when I click on for example a comment that contains a URL to a different website (on which the connection is not encrypted), then the padlock on Youtube changes to yellow.
Also, when I`m on some website that isn't secure, If that website has, for example, a Paypal link on it, when I click on that link (that is secure) the page that had no green padlock, suddenly has one.
Is this a problem? Can this become a problem? Is the user becoming vulnerable to some attacks, and if so, which one? Can you explain why the padlock changes like this.
Tested on Firefox Quantum (Windows 7) and Chrome 63 (Ubuntu 16:10).