Try harder - This isn't installable in Pale Moon 25.4.1 (x64) although support reportedly exists for Pale Moon. Figure this out.
(These instructions are a little dated..)
When installed, it will prompt to download ffmpeg. While ffmpeg is depricated and replaced by avconv, it is still just fine. I'd rather have it download what it expects to use, to avoid any issues.
- UPDATE - I pointed its ffmpeg binary to /usr/bin/avconv and it is working well.
- This is untested on Windows. I'll update this if I get around to it.
REQUEST - They have all of their checkboxes on the right. They should be on the left.
- Preferred file format: [WebM]
- Select video quality: [HD1080p]
- Select download folder: [Custom]
- Custom download folder: 
Download video files using keyboard shortcut:
- This will make it invalid, and disable it.
Try to keep toolbar button visible: [_]