Rated 4 out of 5 stars

Excellent, but if the user could define the shortcuts for the search engines, for instance, I have one search engine: "cplusplus", if I could make that "@c++" or "@cpp", that would be the ultimate. True I can just "@cp" but thats kind of awkward.

This review is for a previous version of the add-on (0.3.1b). 

Use keywords

You can already define keywords for search engines using "Manage Search engines"