Mozilla has blacklisted unpatched versions of the Java plug-in from Firefox on Windows in order to protect its users from attacks that exploit known vulnerabilities in those versions. Mozilla can ...

In October 2009, Mozilla decided to add Microsoft’s Windows Presentation Foundation (WPF) plug-in to the Firefox blocklist after Microsoft revealed that it had a vulnerability.

If you're still using Java and Firefox, make sure you're on browser's the latest version to be protected from the most recent vulnerabilities in the plugin.

Mozilla can add extensions or plug-ins to the Firefox add-on blocklist if they cause significant security or performance issues.