the portable version can be run whilst a fully installed version is in use.

hmmm,
just tried:
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Mozilla Firefox, Portable Edition | PortableApps.com
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Another instance of Firefox is already running. Please close other instances of Firefox before launching Mozilla Firefox, Portable Edition.
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OK   
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does anyone know, is there maybe a different version of FFportable ? or does it have to be on an external drive or something (doesnt make any sense to me but cant think of any other reason..)

Here you go tomo man: link.

Ehtyar.

thanks Ehtyar