Save ~700k of RAM by initializing default values with a local JSON object vs repeated function calls, while creating defaults only need to check for null, .getItem never returns undefined, using bracket notation to get localStorage variables like ["value"] can return undefined though.
Instead of setting the background image inline while appending html, call it after to prepare for setting the "background-image" with a thumbnail I generate.
Also removed the extra <div> that was named imgwrapper, it isn't needed anymore since only one div is needed to encapsulate the image/folder icon.