Another add-on for Firefox for downloading videos from YouTube pages is
DownloadHelper. The add-on works in Chrome as well and also will allow
you to download videos from other sites as well as the YouTube site. Like
Download YouTube Videos as MP4 extension, it allows you to select from
various resolutions for the downloaded video, so you can trade off resolution
against file size, i.e., a higher resolution and larger file size or a lower
resolution and smaller file size.