It seems that Adobe didn't update the flashplayer-win.xpi file to 10.1, which this installer depended on.
So you should copy the flash 10.1 plugin installed on your computer's hard drive into your Firefox Portable plugin directory. This solution isn't as good as the original, but since it seems that Adobe is not updating the xpi file anymore, it is better than doing it manually every time.
1. Open Notepad
2. Paste the following code into notepad:
copy %WINDIR%\System32\Macromed\Flash\flashplayer.xpt App\Firefox\plugins /Y
copy %WINDIR%\System32\Macromed\Flash\NPSWF32.dll App\Firefox\plugins /Y
3. Click File and Save, browse to [your usb key]\PortableApps\FirefoxPortable (or wherever you have Firefox Portable installed), then under filename type "update_flash.bat" (with quotes)
4. Make sure you have the latest version of Flash Player installed on the local computer. Download and install it if necessary.
5. Browse to [your usb key]\PortableApps\FirefoxPortable (or wherever you have Firefox Portable installed) and double click on update_flash
6. Open Firefox Portable and go to
to check your Flash Player version.
My hope is that this continues to work with future versions, so that when you update Flash Player on your computer, you can just run this batch file to update the Flash Player in Firefox Portable.