I don't usually recommend anything less than transparency but... DAMN.
I could give you long flowing analysis, but I'm not going to do that at this point.
Here's the deal. I'm guessing this is a two month blip on your timeline. I hope you are NOT a big social media poster. (Kids, this is why social media is not your friend). If you are big in social media about this prior spot, scrub it. Now. Nursing can be a small community in some "circles" and word of mouth is a real thing. I hope not in your case. If you have some anominity, now is the time. Use time wisely. Go meet with a former prof you were on good terms with - as a FF/EMT you might be a "known quantity" and that can cut both ways, but if you have any good contacts in even a small ER, now is the time to use them. You need to find a job. A residency. ER anything. Somewhere. Now.
The way you were talked to is unnecessary. Just ignore it as meaningless. Move on, it reflects more on them than you. I've seen toxic workplaces and bad actor managers, but wowza. Just go to LTC. When they crap on other nurses as "less than" for critical thinking that tells me everything I need to know.
I might just be so traumatized over the way I was "essentially terminated" I could become amnesiac over the entire event. Kinda a PTSD thing -- I've not been dishonest, but that was brutal for essentially a systems issue and I just cannot imagine a manager speaking to me like that. No. Like just forget the entire thing. Move away if necessary. Not even kidding. You could list it and reference it and just say it wasn't a good fit and it was a difficult decision, but the right decision.
Not sure what your situation is, but the FF/EMT thing might be coming into play here (I'm sad to say that, but it has happened to many). Somehow, when other nurses know that is your background, it has the potential to make the transition unnecessarily "unpleasant" be it deserved or not. Just my opinion and experience.
Honestly, I have also worked with several EMS'er who did not shut up about their backgrounds - including one who was not here to be getting "bedpan experience" and being ready to run trauma - and thought they were so bright as new nurses and I could not find reasons fast enough to see that they were shown the light or shown to the parking lot. I say that only because of my background. I never mention my FF/Medic/Flight background when I go somewhere new - ever.
Also, some new nurses spend a lot of time talking about their "goals" - this is a big NO-NO when you don't get your "dream job" or you are DOING TIME till you can apply for CRNA school.
Stop it, kids.
I'm just "here" till I can get to ________. This is not cool.
You are where you are with others that are giving it their all.
When you pull this horsecrap, it immediately lets everyone you are working with know that you think you are "passing through" "too good" "better than them" or what the heck ever. That the unit you have to be on, the one they work on is someone... undesirable. It's gonna put a target on your back. You might be good, competent - but that's just part of being a nurse and as a new grad or newer grad, I'd suggest if anyone (not implying the OP did this, just general advice for the future as so many find themselves in these situations) is doing this, you are setting yourself up for failure.
I 100% AGREE WITH PIXIE.RN -- YOU DO NOT NEED ICU EXPERIENCE TO WORK IN THE ER. NOT EVEN SURE WHERE THAT IDEA WOULD COME FROM.
Find an ER residency or ER new grad spot double quick. Anywhere if you are mobile. Cast a wider net. New grad, prior EMT (only to hiring folks not to PEERS ever). Your long term goal is to just be a good nurse in 6 months. Love the ER. THATS ALL FOLKS.
Either tell any NEW JOB folks about your prior nurse job and resignation/fired experience (I hope you resigned) or not - it wasnt a good fit, I enjoyed patient care, focus on what you learned. If you have resources consider taking ACLS on your dime. Buy an Essential of Emergency Care (ENA Publucations). Join ENA. Take TNCC and ENPC (Trauma and Pedi classes). These may help you land an ER spot and you will meet ER folks.
Also, most of this is general advice as many read these posts - social media can haunt you. Stay off the net about it. Really.
Keep your head down and mouth shut, and just get it done - is still good advice, still applies. Keep your business, your business.
Things will work out OP. Just give it another try, fit matters.
6 years of FF/EMT ... MATTERS. Give it another try with different tools.