Febrile seizures are incredibly scary. My oldest daughter (almost 5) has had two of them and my middle son (2.5) has had one. We have a very strong family history of them. I take a lot of comfort in the fact that most kids outgrow febrile seizures by the age of 5 and that febrile seizures themselves are not life-threatening. Very scary to witness, but not life threatening.
It took some time for me to learn to relax about the next seizure. After my daughter's first one, I felt like I was one of those paranoid mother's that was hyper-alert to the smallest thing, just waiting to see if she was going to spike another sudden fever. As you gain some distance from the seizure, it gets easier to let your guard down. It has been a few years since my daughter's last seizure and the more time that goes on, the less paranoid I feel about her having another one. It helps that she is at the age where she has probably outgrown them. I find that I worry more about my son having another one because he is still young and tends to get sick more frequently than his sisters.
Logically and rationally, there isn't really anything that you can do to prevent a febrile seizure. A febrile seizure usually comes on suddenly, with very little warning. Keeping your kids away from every child that has the slightest runny nose is not necessarily going to guarantee that your child never experiences another febrile seizure. Not every illness is accompanied by fever, not every fever results in a febrile seizure. I don't go out of my way to expose my children to germs, but I also try to recognize that some exposure to germs is good for building a healthy immune system. It just isn't practical or realistic to think that we can prevent our kids from ever catching an illness. I know that there are parents that bring their sick kids out, but I'd like to think that the majority of parents know to keep a truly sick child at home. I'd be willing to bet that the majority of runny noses and coughs we see are just run-of-the-mill colds. We try to reduce our risks by washing our hands frequently and making sure that we take care of our bodies by staying hydrated and getting enough sleep. To me, that type of behavior is proactive without the paranoia.
Focusing more on how I would react/respond if my children have additional febrile seizures rather than trying to prevent them gives me more peace of mind than anything else. I have been certified in CPR and First Aid for many years and know that I have the skills to deal with an absolute worst case scenario should it happen. Since I can't prevent a seizure from happening, all I can do is arm myself with what I need to deal with one if it occurs again and do my best to keep calm in the moment. I also take comfort in knowing that in our family, everyone eventually outgrew their febrile seizures and nobody seems to have any lasting effects from having them as children. It helps me put things in perspective.
((hugs)) to you, I know it is a scary situation to go through as a parent.