Deleting all System files for Firefox portable installation?

I've got the annoying instance where on every opening of the browser, there is always a 'notification' that updates are being installed.

It flashes for 5 or so seconds, then the browser opens as normal.

Copied the installation to a different drive to test, and it opened fine, with no 'update' on start.

So I'm assuming that there is some sort of residual file that needs to be deleted in some sort of hidden folder.

Where would I find such hidden folders?