Horizontal Auto Arrange
When this flag is set to true, buttons/links with the auto-arrange property set to true will be arranged horizontally. Buttons will be moved to fill any gaps, including any buttons on a previous row.
Example:
pui["horizontal auto arrange"] = true;
When you use this option, you must set the buttons per row option.
You may also need to adjust the button spacing.
Where do you save this configuration option? Here