With TMP 0.4.0.4pre120724a on Firefox 14.0.1 on WinXP Pro I have the problem, that (also since some time) sessions don't get saved or loaded on startup. Looking at the TMP settings shows, that it's set correctly there.
In the error console I see the following message appear every 7 seconds:
Zeitstempel: 20.08.2012 09:48:11
Fehler: TelemetryStopwatch: key "FX_SESSION_RESTORE_COLLECT_DATA_MS" was already initialized
This lead me to this Firefox bug: https://bugzilla.mozilla.org/show_bug.cgi?id=732874. May that be related?