Even if you bring up the default context menu by holding down Shift, you can't save YouTube videos from the context menu. They're made up of two separate streams, one video and one audio. They're sometimes further split into segments. The best way to save them is youtube-dl, maybe paired with External Application Button. Other than that, YouTube Video and Audio Downloader can fetch most 1080p+ streams and mux them via ffmpeg.
[https://addons.mozilla.org/firefox/addon/youtube_downloader_webx/](YouTube Video and Audio Downloader) is clean, doesn't nag you for money, and can mux most 1080p+ streams with ffmpeg.
Alternatively, youtube-dl can be launched with External Application Button.
For YouTube, I use YouTube Audio and Video Downloader. It's clean, it doesn't nag you for money, and it can mux most 1080p+ streams using ffmpeg.
For other sites, I use Video Downloader Prime.
If you chose to download high quality files you'll have to combine video & audio channel:
ffmpeg -i video.webm -i audio.webm -c copy output.mkv
YouTube Video and Audio Downloader and Audio Downloader Prime can show the bitrate. For the latter, you have to first enable the setting in the options page. You also need to lower the default detection size, since it's too high for Soundcloud for example.
I see no way to get this information from Firefox itself, unless the site decides to provide it via something like a custom context menu.
YouTube Video and Audio Downloader is clean, free, doesn't nag you for money, and can mux most 1080+ streams using ffmpeg.
Supposedly the aforementioned youtube-dl can handle those few 1080+ streams that YVAD can't.
YouTube Downloader Lite was pretty nice as I recall, but it doesn't handle 1080+ streams at all.
Anything else isn't worth bothering with, in my opinion; believe me, I've looked and looked.