firefox addon - Intercept/handle mime type/file

Question

How do you disable the default action for .torrent files/content-type application/x-bittorrent(eg open with dialog or run program) and instead handle the data in a extension?

Answer 1

There are multiple ways, that all boil down to nsIMimeService/nsIHandlerService and nsIMimeInfo and setting the appropriate nsIHandlerInfo. E.g. see PDF.js making itself the handler for PDF files (by effectively disabling all handler or plugins and implementing a stream converter), or my answer on how to register a web protocol handler (not mime related but protocol related, but the handler info stuff still applies).

Depending on how you'd like to handle things, you may use the nsIHandlerApp-ervied interfaces e.g. to pass the uri (protocols) or file (mime) directly to some local or web application, or implement a full blown stream converter like PDF.js.

In theory, it would be also possible to implement new kinds of nsIHandlerApp-derived interfaces, implementing in particular launchWithURI (protocols) or launchWithFile (mime content types and file extensions (downloads)). However, this is a bit tricky as nsIHandlerService only handles the built-in interfaces.