Alright, so we have a final Firefox Portable 3 test before release (which is happening worldwide soon) just to ensure our Session Store enable/disable is working properly. Grab it here:
It installs over your existing FirefoxPortable directory. It includes a selection to enable or disable Session Store in the launcher that will fire up if you haven't picked before. It'll set it appropriately in your prefs.js. A utility to reset it is coming in the next 30 minutes.
Also, this new launcher will backup and restore your APPDATA\Mozilla\Extensions and APPDATA\Mozilla\Firefox\Crash Reports directories on the local PC. This way it won't leave anything behind even when FF3 is installed locally (which we have to worry about after today). If you set AllowMultipleInstances to true, it'll still leave this stuff behind though (since it can't keep track of what's what). Please double check this feature as well.
Report back ASAP!