The leaves in the photo resemble those seen on Honeycrisp apple trees exhibiting zonal chlorosis also known as Honeycrisp Leaf Mottling.  

Compare here:

https://www.ndsu.edu/agriculture/extension/extension-topics/gardening-and-horticulture/trees-and-shrubs/apple-trees/diagnosing-apple

https://www.ontario.ca/page/commercial-production-honeycrisptm-apples-ontario#section-5

However, this condition isn't commonly seen on Fireside.

If you are sure the tree is a Fireside, we recommend asking the University of Minnesota Plant Disease Clinic to diagnose the problem.  Go here to learn how to prepare leaf samples and where to take or send them for testing:

https://pdc.umn.edu/

Although it's less likely, based upon what we can see in the photos, potato leaf hoppers might have damaged the leaves.

https://fruit.wisc.edu/2017/06/23/potato-leafhopper/