FreeMDZ Bookmarklet is a shortcut that can help to download music , like browser plugin, but it doesn't have as many permissions as plugin.
Bookmarklet is a link, like other bookmark you stored in bookmark bar. so there is no risky to use Bookmarklet to download music. With bookmarklet you can download music with only need two click, so it can ease use and fast to download.
For first time use, it need just four steps, and only two steps if already dragged bookmarket to your bookmark bar.
Step 1: Show bookmarks bar
Chrome press ctrl + shift + B
Firefox first press alt + V, then press T, last press B
Step 2: Drag bookmarklet to bookmark bar
Step 3: Watch Videos and click bookmarklet
Go to your favorite video site and watch videos eg:https://www.youtube.com/watch?v=eNLjdPI9zdE
Then click bookmarklet, for download
all supported site see: Support Site
Step 4: Download the music