When is detected, add links for download video files in the "messages" section of new design of Youtube.
Note: Youtube not "change" page but reload+edit url for reflect the new page requested. In this mind, when user visite YT, the script start and always check content. But some page not need video links (front page, settings etc...) and some time the messages box is removed/edited. The script change since 0.5 can help to work with this change of Youtube new design. If you can't see any message from this script, just refresh the page (F5) and script start again.
Since 0.5.1, link to GenYouTube added for more formats and alternative when script fail. No affiliation, GenYoutube have many ads, but work.
Since 0.6, We use 2 sources for find downloadable files. And also, don't need to "save target as" with the right click, just click on the link and is downloaded like any other files.