Just a tip for downloading videos off of websites. In chrome (probably similar with Firefox), right click on the page, click inspect element. Then click the Network tab and refresh the page, and make sure the video is playing. You'll see things load in the Network tab, and you're looking for a line that keeps loading. Find it, and copy the URL to another tab. That'll load the video in a way that you can right click and save it. It may be necessary to close the original tab to get the video to load.
This won't work for some websites like Playvid, however. They stream differently. You can however load a Playvid video in http://www.tubeoffline.com, and proceed with the method above.