NSIS Error and an update question.

Using:
WinXP Pro with SP2
PortableApps Menu 1.5.2
Firefox 3.0.9

I've been using this combination for some time with no problems. A recent attempt to open Firefox returned the error message---nsis error: failed integrity test. Other apps opened and ran correctly.

I shut down and restarted the system and Firefox opened normally (I'm using it now).What happened? Is this likely to recur? I would expect an installer to be deleted after installation.---why is it still Present?

I intend to upgrade to 3.0.10 soon. Is that a "non-destructive" upgrade to 3.0.9, retaining config settings, bookmarks, extensions and add-ons or a new installation? If it is a new installation is there an easy way to save and re-install the config setting et al or must I do it all over again?