How to configure Automator to log into a website, each time generating a new random UID and email address?
Try running a script like this in AppleScript Editor:

do shell script "jot -r -c 24 a z | rs -g 0 8"
tell result to set {user, mail} to {paragraph 1, paragraph 2 &amp; "@" &amp; paragraph 3 &amp; ".com"}

open location "https://accounts.google.com/ServiceLogin"
delay 1
tell application "Safari" to tell document 1
    do JavaScript "document.getElementById('Email').value = '" &amp; mail &amp; "'
    document.getElementById('Passwd').value = 'password'
    document.querySelectorAll('#gaia_loginform input[type=submit]')[0].click()"
end tell


For Chrome, replace document 1 with active tab of window 1 and do JavaScript with execute javascript.