Rated 4 out of 5 stars

The add-on is polluting.

Error: Components is not defined
Source file: chrome://canitbecheaper/content/invisiblehand.js
Line: 48
aSubject = aSubject.QueryInterface(Components.interfaces.nsIHttpChannel);

Components is not always available.
It is however always available for aTopic is http-on-examine-response and http-on-modify-request
So, make sure to check for those two first before trying to access Components

This review is for a previous version of the add-on (1.8.2).