If you don’t have a wedge…get a stiff piece of plastic (Pocket comb with a thick handle works fine) and then the coat hanger, I use an Antenna. Jam the comb between the rubber on the pillar and the window. Pry back just enough to make a gap between the rubber and glass. You won’t break the window as long as you don’t hit the edge with the antenna too hard. So be careful. (OT an easy way to break a window, if it is rolled down a little is to take a screwdriver, with a pointed shank like craftsman flatheads, and just drag it along the top edge…instant breakage) Anyways, now pull the lock. Not sure what the Mustang has as far as a little flippy lock swtich or something to pull up on. Or just hit the unlock button. I have done this many times to open junk cars at M&M before but only on cars without the frame around the window. Antenna works best because it is pretty stiff unlike a cheap coat hanger.
This is an old skool trick someone showed me. Takes about a minute to do. Pretty scary how easy it can be to break into a “older” car with a god damn pocket comb. Snap off the antenna, bend the end of the antenna(some antennas are a BITCH so you may need pliers), jam your pocket comb in the window, pop the lock, and you are in. Older style Neons are the easiest to do this to.