Dave uses Firefox and the favorites get lost from time to time. Leo says that can happen if he uses Firefox Syncing. There is a bookmark management tool within Firefox. Open the sidebar and select bookmarks (CTRL+B). He can then search for the bookmark he's looking for. It's very easy to hide a folder or bookmark by accident. CTRL+B can help him find them again. It could also be that he accidentally deleted them. Dave also uses Time Machine to save to his Western Digital Passport. But now it won't let him back up to it unless he formats the drive. Leo says it's possible that Dave has run out of room. To format, use Disk Utility. But be warned, that will delete the backups. He recommends saving those backups to another drive before he formats them.