Flash Plugin for Portable Firefox

Flash Plugin for Firefox Portable Download Here for FREE

When run, it'll download the plugin from Adobe's server and install it into your copy of Firefox. You just select your FirefoxPortable directory in the installer and it does the rest.

or you can manually place the *.xpi file on the extension folder, here is the link Flash XPI

If the above fails, try the alternate (and more geeky) method:

1. Install the plugin in a local copy of Firefox (on your hard drive)
2. Locate your plugins directory (usually C:\Program Files\Mozilla Firefox\plugins\)
3. Copy the plugin you need from there to your FirefoxPortable\Data\plugins directory (Some Exmaples: For Flash, copy NPSWF32.dll... for Shockwave, copy np32dsw.dll)