If you use disposable email addresses (in particular Harakirimail.com) then you might like this workflow.
Type "hara" followed by the name of the mailbox that you want to create, hit Enter and a new tab will open in your default browser with your disposable mailbox and the email address will be copied in the Clipboard, ready to be pasted
Download : http://goo.gl/YafPaK
I will post updates if there are any, feel free to post your suggestions and advices
Marco