macOS Sierra: Safari dialog opens with no buttons
Make sure Safari is closed when preforming this operation.


Go to ~/Library/Safari/
Drag the Bookmarks.plist to your Desktop
Move all other files and folders in ~/Library/Safari/ into your trash
Open Safari and then immediately quit out
Replace the Bookmarks.plist in ~/Library/Safari/ with the Bookmarks.plist that you saved on your Desktop in step 2
Open Safari and see if the problem persists