My default web browser is Firefox. I recently uninstalled Internet Explorer 11. Subsequently, registry cleaner decided to delete the key: Open with Application Issue "C:\Program Files\Internet Explorer\IEXPLORE.EXE" -nohome HKCR\htmlfile\shell\open After doing this, html files could not be opened. I restored this key and html files now open in Firefox. It seems reasonable to delete this key, since it points to a non-existent file. However, it seems that Windows automatically redirects a request to open an html file to the default web browser. CCleaner should not delete this key. I am running CCleaner 5.77.8448 in Windows 10 1909.