Set the defaultPageTransition global option if you'd prefer a different default transition. Dialogs have a different option called defaultDialogTransition that can also set configured.
By default, transitions are disabled when the window width is greater than 1000px. This value is configurable via the global option $.mobile.maxTransitionWidth, which defaults to 1000. The option accepts any number or false value. If it's not false, the handler will use a "none" transition when the window width is wider than the specified value. This is useful because transitions get very wonky on wider screens.