I'm not a regular updater of CCleaner, so I don't know what my previous version were, but last night I updated to v5.51.6939 64-bit on my Windows 7 HP 64-bit machine, and proceeded to do a cleanup. Under "Thunderbird" I had these options selected: Internet Cache, Internet History, Download History and Last Download Location. When I started up Thunderbird again, everything in it was gone (!). Fortunately the profile (along with most of its files, e.g. e-mails, etc.) was intact on my hard drive. At first I thought that Thunderbird just forgot where the profile folder is, but it turned out that Thunderbind knew where the profile folder is, but something got corrupted or missing from the profile folder. I tried setting up a new profile using the standard Thunderbird instructions, but it wouldn't work (meaning one or more files in the existing profile got corrupted or missing). I eventually managed to restore Thunderbird, by the way.