I have been facing this issue on one of my client's Magento website.
On Magento admin panel WYSIWYG editor, when I click on Inert image icon and browse button, the Insert Image... pop up appears.
It displays the left side tree structure but the images are not displaying on the right side. Please refer to the screen shot.
I have 777 permission given for media folder and files.
I have cleared cache folder.
When I log the getStorageRoot() function, it returns,