probably not fire blight, maybe graft failure. Usually fire blight leaves hang on and eventually turn brown leaves do in the fall. Also, there is the shepard's crook and the brownish liquid that may be seen early on when a strike hits. Fire blight enters through the blooms or hail injury. It's a little late for fire blight to start unless one of the above conditions have occurred.

I just had an apple tree do the same as you describe and it was not fire blight. I removed the tree as I do not care to watch slow death and I can use the space for a new tree.

Not fireblight. Could also be apple scab, although that usually presents much earlier in the growing season, at least in my neck of the woods.

Probably have to send leaves into diagnostic lab if you want it nailed down with precision.

+oM