I've just download Thunderbird Portable and tried to set up some configuration on ThunderbirdPortable.ini file, as usual with portableApps applications (in special disabling the Splash Screen).
But it turned out that the .ini file provided with Thunderbird Portable 3.1.7 Rev 2 on ThunderbirdPortable\Data\settings\ThunderbirdPortableSettings.ini wasn't working:
[ThunderbirdPortableSettings]
AgreedToLicense=YES
I've found that the problem was that file name and its first line contained the word 'Settings'. Renaming the file to ThunderbirdPortable.ini and the first line to '[ThunderbirdPortable]' solved the issue.
So I'd suggest changing the .ini file packaged with Thunderbird Portable.
Regards
The settings file is unrelated to disabling the splash. It is used internally by the launcher to track paths for update. An example ini is included in the other\source directory. Nearly all apps in pa.c format operate this way.
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