Some YouTube videos are flagged by the community. They are usually about sex, violence or hateful content. To view them, you need to log-in first for the age verification. If you are aware of privacy and do not want to log-in, you can download an extension add-on You Old Enough for Firefox. It is an experimental extension so you need to have a Mozilla account first.

When you want to watch flagged videos, You Old Enough will pop up a new video like above. You can now play the video without logging in. This prevents the viewing history to be recorded to your YouTube account. Feel better?

[via gHacks]