This is something between desktop and web, but you could use Chromium Embedded (http://code.google.com/p/chromiumembedded/). It uses GTK+ on Linux, Cocoa on Mac OS X, and it's own library on Windows (but it looks identical to Windows' UI elements).
This is already done in Brackets, you could just copy/paste the code from https://github.com/adobe/brackets-app/blob/master/src/win/ce... and https://github.com/adobe/brackets-app/blob/master/src/win/ce... as it's under MIT license.
With the bridge in place you can access files from JavaScript as follows:
brackets.fs.readFile('path/to/file.txt', 'utf-8', function(file) {
console.log(file);
});