Thank you for confirming. Unfortunately macOS 10.13.6 High Sierra is very likely the root cause of what you are seeing.
Firefly is a modern web application that requires an up-to-date browser to function correctly. On macOS 10.13.6, all major browsers — Chrome, Firefox, Edge, and Safari — have dropped support and are no longer receiving updates. The versions of these browsers available on High Sierra are now several years old and lack support for the modern web standards that Firefly depends on to display generated images. A blank screen is a typical symptom of this incompatibility.
Firefly's technical requirements, including supported browsers, are documented here: https://helpx.adobe.com/firefly/web/get-started/learn-the-basics/technical-requirements.html
Note that Adobe specifies browser requirements rather than minimum OS versions, since Firefly is a web application. The issue on High Sierra is that no supported modern browser is available for that OS version.
The only reliable solution would be to upgrade to a more recent version of macOS. Apple currently supports macOS Sequoia, Sonoma, and Ventura. Upgrading your operating system would allow you to run a modern browser and use Firefly as expected.
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