The lock means that the website you’re using is encrypted, so that even if someone is watching your browsing on the network (like another person on a public WiFi hotspot), they won’t be able to see your password. { -brand-name-firefox } will try to warn you when you’re about to enter your password on an unencrypted site.
该锁表示您正在使用的网站已加密，因此即使有人在监视您在网络上的浏览活动（例如同一公共 WiFi 热点上的另一个人），他们也无法获取您的密码。{ -brand-name-firefox } 会在您将在未加密网站上输入密码时尝试警告您。