13. A computing device comprising: one or more processors; and one or more computer-readable storage media comprising computer executable instructions stored thereon that, responsive to execution by the one or more processors, cause the one or more processors to: receive a call from a third party object that requests a domain context; ascertain the domain context of the third party object; return the domain context to the third party object; require the third party object to include its associated domain context in subsequent calls that the third party object makes; receive a subsequent call from the third party object; ascertain, from the subsequent call, the domain context of the third party object; and make a domain context-based decision based on the ascertained domain context by refusing to allow the subsequent call to execute if the third party object's ascertained domain context does not match a target window domain context or allowing the subsequent call to execute if the third party object's ascertained domain context matches the target window domain context.
13. A computing device comprising: one or more processors; and one or more computer-readable storage media comprising computer executable instructions stored thereon that, responsive to execution by the one or more processors, cause the one or more processors to: receive a call from a third party object that requests a domain context; ascertain the domain context of the third party object; return the domain context to the third party object; require the third party object to include its associated domain context in subsequent calls that the third party object makes; receive a subsequent call from the third party object; ascertain, from the subsequent call, the domain context of the third party object; and make a domain context-based decision based on the ascertained domain context by refusing to allow the subsequent call to execute if the third party object's ascertained domain context does not match a target window domain context or allowing the subsequent call to execute if the third party object's ascertained domain context matches the target window domain context. 19. The computing device as recited in claim 13 , wherein the receiving the call that requests the domain context is performed by a web-based email application.