I have written a Firemonkey app and it saves its files with extension ".qrmx".
In both Explorer (Windows) and Finder (Mac), its thumbnail looks like a blank sheet of paper with the top right corner curled over. This is, I think, the generic thumbnail. How can I introduce a thumbnail specific to my app?
It finally dawned on me that I needed to associate my program files with my program. For Windows, I was able to do this within the Inno Setup installer by defining Registry settings. For OS X, I was able to do it with settings in the info.plist file. Both operating systems then used the appropriate icons from my app.