Videos that stream in flash players can be downloaded in Firefox browser by means of an add-on called Video Download helper. You can download it from addons.mozilla.org.
This add-on notifies you of any possible downloadable content from the webpage you are viewing. It also enables you to download them directly.
You can also copy the downloadable content’s URL and put it up for faster download in a download accelerator.
The next time you are playing a video in your browser, video download Helper will help you to download the content.