What if I'm not have firefox, but have Google Chrome?
It's simple! You also may change User-Agent in Chrome, but even without installing any plugins, you just have to run google crhome with additional command line argument (you can use this instruction if you don't know how do that in Windows).
You should run
chromium-browser --user-agent="Mozilla/5.0 (iPhone; U; CPU like Mac OS X; en)"(replace "chromium-browser" to whatever applied for you like "chrome.exe" or "google-chrome" depending on version)
and than simply open http://wave.google.com now all waves will be ready to print or even to export to pdf if you decide to print waves into pdf files :)