Remove wildcard from Postmessage

[HunnySajid]

Currently we are using wildcard '*' while communicating with postMessage. It is not correct as it broadcasts messages to all.
We need to fix it so that communication can only be between out content script and webpage.

Relevant links:
https://developer.mozilla.org/en-US/docs/Web/API/Window/postMessage#using_window.postmessage_in_extensions_non-standard

[HunnySajid]

Here I have broadcasted a postMessage with select-identifier from webpage. I setup another extension that listened to this and alerted.
As postMessage is using wildcard, the select-identifier messages was broadcasted to every window. It could be exploited.

Video: https://www.loom.com/share/755f78a875f340a4a818da3c602e1f73