I got this in my Gmail inbox the other day: "Thank you for signing up to give us early feedback on Google Wave. We're happy to give you access to Google Wave and are enlisting your help to improve the product". Since I'm all about making improvements, I clicked the link to accept my invitation to Google Wave. Once I signed in with my handy dandy Google account (OK, so I'm going a little overboard here), Google Wave opened in my Firefox browser.