Running CCleaner closes Windows Photo Viewer in CCleaner Posted July 29, 2017 any reason not to update to the latest version of CC and see if it still happens? Thanks. Ok it gets even more confusing: - Installed latest version: Didn't work - Unchecked "Windows > Windows Explorer > Thumbnail Cache": Worked - Rechecked "Windows > Windows Explorer > Thumbnail Cache": Still worked - Waited 10 minutes and opened Firefox: Didn't work again. I could screen capture it with a video showing what steps I take and post it as a link if that would help. Please let me know if you need any more info about my computer or what I am doing. Thanks.