- Download Optifine
- Open FTB Launcher
- Click on the "Edit Mod Pack" button.
- Click the "JarMods" tab.
- Click the "Add Mod" folder.
- Browse until you find the optifine .zip file, click it and then click on the "Open" button.
- Verify that optifine is in the "Enabled Mods" section of the "JarMods" tab.
- Close this window, and launch the game.