Download and install the Google Voice Search App. Just install the App and select Done. No need to open it as it should interface with any App that supports voice search. Side Note: Opening the Voice Search App directly will allow you to do a Google search which defaults to the web browser.
Google Voice Search: http://www.1mobile.com/voice-search-79945.html
I verified Voice Search works on the Fire HD with the Merriam Webster Dictionary App (http://www.amazon.com/Merriam-Webste...rds=dictionary
) available from the Amazon App Store.