Usually that is malware, but to be safe, do the following:

• Update Firefox Update Firefox to the latest release
• Scan for malware Troubleshoot Firefox issues caused by malware
• Update your plugins, http://www.mozilla.org/plugincheck/

Whenever you get a message / popup that software / files need to be updated,

DO NOT USE ANY OF THE PROVIDED LINKS.

While this may be a legitimate message, it could also be Malware or a Virus. Any time you want or need to check for upgrades, go to the web site of the True Owner of the program in question. For example, to check out Firefox, go to Mozilla.org.