Kaner YouTube Downloader by Himanshu Sharma

This add-on which will allow you to download YouTube Videos with all available options (audio-video, video-only, audio-only).

This works with latest Youtube site settings. If available from youtube, it allows user to download up-to 4K resolution videos at 60 frames per second. For higher resolution, youtube provides separate video and audio streams. Since this add-on works directly with youtube framework, user will have to download video and audio separately and merge themselves.

It reports the audio/video resolutions, file-formats and the size of files, so that it is easier to choose the best variant.

This add-on runs without sending/fetching any information from/to third-party sites and respects your privacy.

If you have any enhancement suggestions OR face any issues, please email me at hims.kaner@gmail.com.


Update: I have recently added add-ons options page.
Filter option - From the options page, user can filter/choose the format/type of files that are available for download.
Auto-download option - When user visits any youtube page, the corresponding audio/video file is automatically downloaded. This can also be selected from options page.


Update:
If you want faster downloads, please try installing the following plugin:

https://addons.mozilla.org/firefox/downloads/file/3937207/ba5ae116fe4f41b88ad2-1.2.xpi