Well, any place where you had to get a key, you no longer have to go there. The doors will no longer be locked (Unless you reset the game), so you can easily slip by. However, the Fire Temple is one of those temples where it is difficult to save and quit unless you want to go through half of the dungeon. A lot of the dungeons in OoT are pretty straight forward, except for the parts in which you must risk life and limb for a key. So, pretty much, there aren't shortcuts, just skipping the parts already done.