Well...I hate to post this, because it makes us look bad; but there needs to be accountability for stuff like this. What happened to you today is complete and utter BS...there is no excuse for it whatsoever...and it's a blatant abuse of privilege.
For those of you who don't know me, I am a firefighter; and damn proud of it. I would and do protect my profession with my life and there isn't a job in the world I would rather have (...except maybe porn star or race car driver.

)
I am not familiar with the laws where you are, but what it sounds like to me is a paid on call firefighter with ruffled feathers. The term "volunteer" is still used, but a true volunteer department is hard to come by these days, if for no other reason, because of liability issues. So, departments that are not large enough to be full-time, have a part time, on -call staff that respond to each call as needed. The majority of these departments allow their firefighters to use POVs (Personally Owned Vehicles) to respond either directly to the scene, or to the station. They are allowed to affix emergency lights to their vehicle to use
only in direct response to a high priority call. In most states, these lights are only allowed to be red, and blue is reserved for police.
I have unfortunately had the disappointment of being involved in this very same issue, only my guy actually tried to pull me over by forcing me off the road...(it didn't go well for him)
I am very disappointed that you had to deal with this today. There is no excuse for some wannabe cop to abuse the privilege his public has entrusted him with, just to exact some road rage, or look cool to his buddies. With privilege and trust comes responsibility.
If you're in an area that has a paid on call fire department, I would give the chief a phone call, or shoot him an email just asking if he has any guys with a '91 impala and red grill lights...
This guy does not deserve to keep them, and I'm sure the chief will agree, since it's his reputation on the line when people abuse it.
-Jack