I only want to initialize the slider (or to start the plugin) when the browser have a specific orientation
You need to do something like this:
if (screen.innerWidth > screen.innerHeight) {
// start orbit when the device is on a landscape mode
$(document).foundation('orbit').init();
}
can I load Orbit content Slides with Ajax
Sure you can, just reinitialize orbit after you added your content. Something like:
$("#yourSlider").append('<li><img src="url_of_the_image" /></li>');
$(document).foundation('orbit').init();