Easy YouTube Video Downloader
Streaming video doesn't work without an active Internet connection. No Net equals no Flash video, so sites such as YouTube are off-limits. Easy YouTube Video Downloader to the rescue: This Firefox add-on allows you to download Flash movies from YouTube and other sites for later viewing with or without your connection. In addition to all the free clips, you can find free versions of full movies such as Ghostbusters on YouTube.
Note: This link takes you to the add-on's page at Mozilla.org, where you can automatically install the file into your Firefox browser.