So far, I've never used my Steemit private active key for an account that I'm not sure about.

Not using our active key on any third party website is one way to keep your account secure. I really love this idea, third party website can become compromised or may be used as a means for Phishing.

Using outdated applications and browsers can become a problem. The designer must have seen a bug or vulnerability before declaring it out of date an needing an update.