The terrafirma.msi file you have requested: Tools and Utilities / Terrafirma / Terrafirma v1.6.8 Installer - 416kb is not available. Perhaps try browsing all files for the game Terraria and upload any files you want to share or are missing. This is the only information we could locate:
Terrafirma is mapping tool for Terraria. It gives block information in the statusbar as you hover, lets you zoom and pan around your map, and can save your map out as a png. New features include textures and lighting. If "Use Textures" is grayed out, it's because the program can't find your Terraria directory.