The FIRST button in the toolbar ribbon appears after installing the WPILib 2014 C++ update (aka Workbench update) available from
http://first.wpi.edu/FRC/c/update/Release/.
Make sure to:
1. Close WB before running the installer/update
2. Ensure the Wind River Registry is no longer running (check the available icons in the Windows system tray and ensure the Wind River Registry is set to appear.)
3. Then run the update.