CCleaner Version: v5.31.6104 (64 bit)
Thunderbird Version: 52.1.1 (32 bit)
OS: Windows 10 (64 bit)
How to reproduce:
- Close Thunderbird (if open)
- Backup your Thunderbird profile data from C:\Users\<Username>\AppData\Roaming\Thunderbird\Profiles to a secure location
- Run latest CCleaner with "Last Download Location" checkbox enabled in Thunderbird application settings
- Open Thunderbird
What happens:
- Thunderbird cannot access existing profile data and shows first startup wizard (no “broken profile files” info or anything)
- Profile data is still there but somehow corrupted, Thunderbird still references correct profile folder but cannot "see" it for some reason
- As soon as you overwrite profile data with your backup, everything works again
Conclusion:
The new “Last Download Location” setting somehow corrupts Thunderbird profile data.
I checked with only this setting enabled, it is definitely the cause of the problem.