It seems that when I take ibuprofen (usually 2 tablets 200 MG) that I have a firmer erection?

It happens to me as well. The less inflammation the better blood flow, plus the blood-thinin effect. I would try to take it every other day at least and take it with plenty of food to protect your stomach.
But if you are looking for the ED effect only, you can take Arginine HCL and L-Citrulline Malate 2:1 instead, which are just aminoacids (not synthetic) and common nutritional supplements and get the same effect, or even better. Plus enhanced HGH production if you take it at night. You can take one of them or both combined. Between 3-6gr per day on an empty stomach 20-30 min before workout or just before going to sleep.
Improving your diet would help a lot. Reduce or eliminate animal product consumption, alcohol, sugar. Increase exercise, etc. So many ways to address it...

Yes, it works. First hand experience.

NSAIDS like ibuprofen are known to "thin" the blood (they have an anticoagulent effect) so it is possible this is what is occurring when you take ibuprofen. ED drugs like Viagra work to relax muscles to allow more blood to flow into the penis. It probably wont hurt you to take a total of 400mg ibuprofen a day if your liver and kidneys are healthy, but you should ask your Dr about doing it long term.