I am a beta tester for Firefly and sadly you can only access it through a web browser and it's not a standalone app like Photoshop.
Even if it was, it would still ask to connect to Adobe as with almost all AI tools, they need their data sets and trained models to work and to keep the software content updated, and no company will share those, and even if they wanted to share, such assets are several Terabytes is size and its hard to distribute them.