Sometimes it doesn’t make sense to have live thumbnail previews while working in Coda. Typically this is due to a reliance on server-side scripts or you’re actively working on a script that may cause performance issues with the thumbnail preview. There are two ways to disable the thumbnail preview:

1. Switch to text-only toolbar mode. To do this, control-click the toolbar and select the Text Only menu item.
2. Open the Terminal application and type:

defaults write com.panic.Coda2 RenderTabThumbnails NO

To re-enable tab thumbnail drawing, change the NO to YES.