Hi @Su san, I'm sorry to hear you are having trouble accessing Firefly after the welcome email. Here are a few suggestions:
Once you receive your “You're in!” email, you'll need to visit https://firefly.adobe.com and click on the “generate” button to get started.
Ensure that you are using the same email address that received the invitation to login. Your email to log into Firefly Beta needs to be the primary email associated with your Adobe ID, it cannot be the secondary one.
You can only access Firefly Beta with a web browser. I'm using Brave browser without any issues so far.
Also, try logging out and back in, clearing your browser cache, and switching to a different browser.
It's much better to access Firefly from a desktop computer, not a phone or tablet, if possible.