The latest version of CCleaner (downloaded yesterday) 3.12.1572 (64bit) complains that Firefox must be closed to clean cache. Firefox is closed and the process is not running. This did not occur with the previous version
Windows 7 64bit
Mozilla problem - not a CCleaner feature.
Firefox and Thunderbird have suddenly got a little more in common,
and the warning should be revised indicate that ALL Mozilla products need to be closed and all their processes stopped from running.
It seems to have started working. I am wondering if it is related to an add on, or maybe as you said to the fact that I have Thunderbird open.
Addons can also run under Plugin-container.exe process - perhaps in the absence of a Firefox.exe process
Thunderbird will prevent CCleaner from cleaning Firefox