One of the reasons behind Firefox's popularity is the availability of a vast library of extensions. Users use them to modify the browser to their liking and make their browsing experience easier and more pleasant. The problem is, unbeknown to them, these extensions are exposing them to risk.

At the SecurityByte & OWASP AppSec Conference in India, Roberto Suggi Liverani and Nick Freeman, security consultants with, offered insight into the substantial danger posed by Firefox extensions.

Mozilla doesn't have a security model for extensions and Firefox fully trusts the code of the extensions. There are no security boundaries between extensions and, to make things even worse, an extension can silently modify another extension.

Any Mozilla application with the extension system is vulnerable to same type of issues. Extensions vulnerabilities are platform independent, and can result in full system compromise.

The researchers believe that the weakest link in the chain is the human factor. Many add-on developers do it for a hobby and are not necessarily aware of how dangerous a vulnerable extension can be...
Researchers have found several bugs in popular Firefox extensions that have an estimate total amount of 30 million downloads from AMO (Addons Mozilla community site). Three 0days were also released at the SecurityByte & Owasp AppSec Asia 2009 conference.
more: Zero-day vulnerabilities in Firefox extensions discovered