Suggestions:
1. Require a gmail account, so that you can
2. Use aliases, so the accounts are actually registered to a real email.
3. With aliases in place, you can do
dummy+ign@gmail.com, to know if you've registered an account with that name and for better organization.
4. Timestamp the console output. That will give people an idea of how fast the accounts are being made.
5. Rather than having a "Create muledump" button, make it a checkbox and have it save the file when all the accounts have finished registering. I didn't do thorough testing, but if you aren't checking for overwriting the muledump file, I would suggest looking into that. Creating 50 accounts and then creating another 50, then overwriting it = 50 accounts essentially gone.
6. (Opinion) Monospaced font in console output looks much nicer!