Firefox 46 的開發版本將會對非 HTTPS 頁面加上警示:「Login Forms over HTTPS, Please」。

技術上來說,是當偵測到頁面上有 input type="password"
的元素時會加上不安全的 icon:
When a page with a password field is not delivered securely, Firefox displays a lock with a red strikethrough in the address bar[.]
不過看起來是在試水溫,沒有打算在正式版本開起來:
There are no current plans to show these warnings to users of Beta and general release Firefox.
這樣就有點可惜了...