Photon will, among other things, require the front-end being able to decide on how to display things to the user based on whether or not a touchscreen interface is enabled. The actual specifics on how this information should be surfaced to the UI layer is unclear, but the work to actual do it should be in here.
I _believe_ there are already a few places where the front-end already knows that a touchscreen is being used somehow, but I'm not certain it gives us 100% of what we need. I'll ask some of our front-end folk.
We have :-moz-touch-enabled psuedo-class, but do we instead want something that says that the touch screen has actually been used in this session? For instance, I use a touchscreen laptop and I don't particularly like UI being huge if I'm using my mouse/keyboard. For the select popup work, we only show larger rows if the menu was opened via touch. I believe this latter route is what we should strive for.
Perhaps bug 1035774 is a good way of exposing this?
Stephen, it would probably help move this bug forward if we knew what kind of responsive behavior the UX team has in mind. Is this only about style changes such as making buttons larger and would you say it's sufficient to know if the device _has_ a touchscreen?