Mozilla’s security team previewed a new set of indicators that will be added to Firefox 51, set for launch on Monday, January 23, and subsequent Firefox versions. The biggest update to the Firefox UI is the addition of a new indicator for HTTP pages with password fields. In a future Firefox version, Mozilla plans to show the same grey lock with a red line for all non-secure (HTV) pages. In-page warnings for password fields on HTTP pages are also set for release on March 6.
Source: https://www.bleepingcomputer.com/news/software/firefox-51-to-show-better-warnings-when-logging-in-via-insecure-http-pages/