Comment 4 for bug 536974

Need to add something to delay loading of thumbnails until the user pauses -- many thumbnails are queued while scrolling in thumbnail view. Implement a priority queue (most visible go to the top, invisible are pruned) for loading thumbnails. Many thumbnails will be put on browser queue, causing visible ones to have large delay. Also an issue changing to non-thumbnail mode while many thumbnails are on the browser network queue.