If it's made with the latest Kindlegen/KindlePreviewer, it will be a dual purpose mobi file: a mobi 6/7 part to work with older kindles and a KF8 part to work with Fires (and the very latest apps supporting KF8). It will also contain the all the source documents (open the final product in a zip utility to see those) used to create it.
Most likely—since you were concerned only with creating a fixed layout ebook for the Fire when designing it—it will still
open on a K3, but will probably look like utter crap on anything NOT a Fire.
