How to create blob: url for local file with FF ext

I'm writing a FF ext which has the filepath to an existing file, and I simply want to create a blob: u开发者_如何学编程rl for the file, without creating an <input type="file" field which the user has to interact with. Creating a hidden <input type="file" element which the user does not need to interact with would be fine.

I have chrome privileges since this is for a FF ext, so is there a way to do this?

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Is this whart you are looking for?