Firefox Portable 13.0.1, Thunderbird Portable 13.0.1 and SeaMonkey Portable 2.10.1 leave behind an empty folder within $LOCALAPPDATA of Mozilla\Firefox, Thunderbird and Mozilla\SeaMonkey respectively. This is a result of a newer version of the underlying engine so the Firefox and Thunderbird 10 ESR releases are unaffected.
The issue has already been fixed in Firefox Portable 14.0 Beta 10 and Thunderbird Portable 14.0 Beta 4 and will be fixed in the next release of Firefox and Thunderbird Portable. As a workaround, you can use the launchers from the current beta releases of FFP and TBP with the stable releases to fix the issue now.
This bug will remain open until the next releases in about 6 days.