From the Mozilla Security Blog:
First things first: If you are reading this post on a recent Lenovo laptop, please click the lock icon in the URL bar, then click “More Information…”. If you see “Verified by: Superfish, Inc.”, you are infected with Superfish, and you should follow these instructions to remove it.
The Superfish adware distributed by Lenovo has brought the issue of SSL interception back to the headlines. SSL interception is a technique that allows other software on a user’s computer to monitor and control their visits to secure Web sites — however, it also enables attackers to masquerade as secure websites, in order to spy on users or steal personal information. Firefox is affected by Superfish, but Mozilla is deploying a hotfix to Firefox that works with other disinfection software to ensure that Firefox is disinfected as well.