There is a postMessage API that websites and extensions can use to communicate over. Many are misconfigured and can allow for 1. Extensions to snoop on sensitive website content 2. Websites to gain access to privileged extension capabilities. Great research!
Chat, I don't want to be that guy, but I think Microsoft has really pissed off security researchers and we're approaching the tipping point.
This Eclipse guy has really rocked the boat for Microsoft.