Section 2 provides a brief overview of the Android OS permission system and examples of vulnerabilities and attacks that target extensions. In Section 3, we present the motivation for this work by detailing vulnerable and malicious extensions we created and found in the wild. Section 4 presents our proposed approach to defend extensions on Firefox for Android against vulnerable and malicious extensions. While Section 5 discusses the related work on desktop and mobile extensions security, conclusion and future work are discussed in Section 6.