- Open dev tools
 
- Search for the 
<video… tag. 
- Copy the source URL
 
- Right click on the 
body tag and click Edit as HTML 
- Add an a link with the src right inside the body tag like:
 
<body>
  <a href="url-you-copied">download</a>
  ...
- Click outside of the editing html to rerender the page and show the download link
 
- Right click on the download link and select "Save as…"
 
- If you can't write click, open dev tools and run this in the console, then try right clicking on downlaod again:
 
document.removeEventListener('contextmenu', getEventListeners(document).contextmenu[0].listener)
  
turn into bookmarklet/userscript plz