Download the following files (Right click and "Save Link as"):
Run the Uninstallers from your Downloads folder, to remove BOTH Flash Player and Shockwave.
Go to: C/Windows/System32 and delete the Macromed folder.
Go to: C/Windows/SysWOW64 and delete the Macromed folder.
Open your Windows Registry Editor (Start>Run or press the Windows key+r. Tpye "regedit" [minus the quotes] and click OK.
In the Registry Editor, go to: HKEY_LOCAL_MACHINE/SOFTWARE and delete the Macromedia folder.
Go to: HKEY_CURRENT_USER/Software and delete the Macromedia folder.
Close the Registry Editor and empty your Recycle bin.
Run the Shockwave FULL Installer first, and THEN the Flash Player Installer. These are offline installers and will require no connection during the process.
If problems persist, try disbaling other plugins and extensions for Firefox, to determine if one or more is conflicting with Flash and Shockwave.