I mounted a dual strobe behind/below my mirror. It wouldn't really fit above. It sits behind and slighty below the mirror, it was a perfect fit and doesn't really obstruct the view, plus it is below the tint line so its brighter. I mounted it with the suction cups it came with and have never had any problem at all with coming off, it is a solid mount. I have taken it off a couple times when I didn't want people to realize the vehicle belonged to a cop and really had to haul on it to get it off.
Before you go too crazy you may want to check the laws on what lights you are allowed to have. In general the police will not bother a firefighter but you might find some that will or if you are too overzealous with your driving you may get complaints on you and the police may have to do something. You would be surprised how many complaints we get on volunteer firefighter's driving, not dissing them in anyway as I used to be one myself, its just that sometimes they can go overboard, just like young cops do. Two months ago a local firefighter who drove a 1980's ford truck all decked out with lights and sirens (that were not legal for him to use) got in a wreck on the way to a call, he is in a mess right now and will likely face several charges.
Not sure about there but in my state firefighters are very limited in what you can have for lights, except for a fire chief. Firefighters are not allowed to have any wig wags/flashers or hideaways only dash or windshield mounted lights. As a police officer I can have hideaways, dash lights, grill lights, light bar etc if authorized by my agency but no matter what I can not have wig wags or tail light flashers in my personal vehicle, seems weird but that the way it is.
The other thing to consider is insurance coverage, will your department cover you if you get in an accident responding to a call in your personal vehicle. I can almost guarentee you that your own insurance company will not.
Just some things to consider, have fun with the lighting mods, ST's look sweet with emergency lights.