What are some alternatives?
FlashGot - FlashGot is a browser extension for Mozilla Firefox that is designed to make it easy to download a whole batch of files in one go. The extension is open source and free to use, but it is no longer compatible with the most recent version of Firefox.
ClipGrab - vanbittern entwickelt individuelle Weblösungen.
Magic Actions for YouTube - Magic Actions is an extension that changes the way you’ll watch videos on YouTube.
y2mate - Y2mate.
Enhancer for YouTube - Tons of features to improve your user experience on YouTube™!
Video DownloadHelper - DownloadHelper is a tool for web content extraction.