Little Rat - a browser extension for monitoring other extensions
"Little Rat is an open-source extension designed for network traffic monitoring. Easily view, monitor, and block traffic from other Chrome extensions on a per-extension basis."
I use it myself and I think it's a very useful extension for everyone who uses more than just few extensions for different purposes and don't fully trust them that they send no data as the developer promises, this extension can monitor the network and act as a firewall per-extension basis.