First, in FF, go to <VIEW> and check <STATUS BAR> if it is not already checked. Then click on CTRL-SHIFT-A and a pane will open showing what, if any, addons you have installed. If NoScript is present as an addon, at the far right of the status bar you should see an white button with a blue "S"; the button my be clear, partially obscured, or have the universal "NO" symbol, overlaid on the "S."
Unless you tell it otherwise, NoScript blocks Flash, ActiveX, Macromedia, et al., scripts. To allow scripts for a particular URL, click on the "S" and a list of URLs will open allowing you to ALLOW those you trust or want.
If we assume that you DLed and installed the correct version of Flash, I cannot think of any other reason why you would get the error message instructing you to install Flash.