Quality of issues with AI generated images

Poorly rendered details.

No AI engine is perfect. They all make mistakes to some degree or another. That goes for Firefly as well as others.

Output must be carefully examined for accuracy and logical rendering, in addition to photo quality.  Often when AI artwork looks synthetic, it's due to subtle inconsistencies that only humans can detect. The fine details are usually where things break down, but not always. Count the fingers and don't allow AI to generate text. 

I'm not able to view any of your images, however I do see that they are PNG format, which should be used only for images with a transparent background.

I also get an error when trying to view your assets. Do these png's have transparent background? If not, they need to be in jpg format when submitting to Adobe Stock.

I get an error with each of your pictures, when I want to check it. 

You will need to check the asset at 100% and correct any error you may see in your picture. Don't expect that because it is Firefly that assets pass more easily. And each AI generated asset has issues that need to be addressed.