It would be nice if extensions could be classified with a rating system for safety.  1 start would be that it does not have any access... and 5 start could be it has full access.  That way the customer can determine which extensions to download.  This will also force developers to make extensions that are of the lowest access level and give users more visibility as to what the extensions are actually doing.   A customers browsing trend is very valuable data for any advertiser.