Yes, the user is notified of that upon installation and has the choice to install or not install. The addon page explains the reason for this permission.

So why the vindictive rating then?

The particular permission to which you refer, "read the content of any web page" is needed in order to search tabs content in the "Search all tabs" feature.

For the record, ATH does not modify any part of any page for spoofing, nor scavenge any user input, in order learn any user information, including but not limited to passwords etc.