Mozilla: User-defined properties on DOM proxies get the wrong "this" object (MFSA 2013-91)

Mozilla Firefox before 24.0, Firefox ESR 17.x before 17.0.9, Thunderbird before 24.0, Thunderbird ESR 17.x before 17.0.9, and SeaMonkey before 2.21 do not properly identify the "this" object during use of user-defined getter methods on DOM proxies, which might allow remote attackers to bypass...

User-defined properties on DOM proxies get the wrong "this" object — Mozilla

Mozilla developer Boris Zbarsky reported that user-defined getters on DOM proxies would incorrectly get the expando object as this. It is unlikely that this is directly exploitable but could lead to JavaScript client or add-on code making incorrect security sensitive decisions based on hacker...