As far as I know, the files from Family Tree/Family Research are proprietary which means no other viewer will work except their official ones. I've searched the website, but I couldn't find anything available for this purpose. The only way to obtain a version of viewer to open the files is through direct contact with the developers.
Access the official website and then click on Get Help on the upper right area of the website. Click on Chat with Us and talk with a representative. He should give you additional instructions: https://familysearch.org/
