tiff images should be displayed in browsers in-place just like other image types.
Indeed. I created issue #6 for the Firefox side of things.
It should be easier then pdf.js extensions, because they also have to display whole separate page and tiff is just one image.
Well, TIFF files can contain multiple images, so it's debatable whether that is entirely true. The spec allows us to just display the first image, but I imagine the bigger hurdle is to just get all the different features implemented.
If anyone wants to contribute code to implement the extensions, it'd be greatly appreciated. But until all the important features are implemented, I'm gonna focus primarily on the standalone JS library. (See also #7 about places where pdf.js and tiff.js may overlap.)
I would be willing to put some time into this library though, if someone else was also working on it :) It is the collaboration that makes it worth it ...