any specific reason why it's chrome-only?
Your example translates the file into a base64 string to send over the unreliable channel, which ends up being a pretty big performance hit compared to a native binary transport.
All of this is to say: WebRTC is getting there, but it's still going to be several months before it's ready for more than demos like this.
I wish developers would honestly stop doing that already. Capabilities and stability are far more important than a logo.
Firefox does have indexeddb, but if you want to do seek operations you're out of luck.
EDIT: To explain more, without seek writing dealing with large files is incredibly expensive, you have to write everything you've got to indexeddb every time you want to modify it.