puemos/hls-downloader ? reverse-engineered prompt

Build me a browser extension that detects HLS video streams on the page as soon as playback starts, then lets me open the extension and see the available playlists in a simple popup.

I want to be able to pick one stream, choose the video quality and audio track I want, then download it as a single MP4 file. It should do the merging locally in the browser so nothing gets uploaded anywhere. Make it work well in Chrome and Firefox, with a clean popup that has a sniffer view, a list of found streams, and clear buttons to select, download, and cancel. If you need to, look up the current browser extension docs online while building it.