Gmail Button allows you to add a toolbar button to your Gmail inbox. You can use this in lieu of a sidebar bookmark or toolbar bookmark simply by dragging it to the Menu or Navibar.
Gmail Button v0.1
P.S. If you open Gmail from a bookmark, you can go straight to New Mail by replacing the target to:
https://mail.google.com/mail/?zx=kksynt1xtviu&shva=1#search/is%3Aunread+in%3Ainbox
Straight from the source, advice from Google will help you master Gmail.
Become a Gmail Ninja

I’m sure many of us must have run into this situation once in a while. In a hurry to do something else we must have forgot to sign-out from our email account. Many times we think we need to get back to the same computer to sign-out. Luckily, if you use Gmail then you don’t have to get back to the same computer to sign-out from your Gmail account. Gmail, nicely, allows you to remotely sign-out from all your Gmail sessions. That means, you can sign-out from all your Gmail sessions from any computer that you have access to.
Learn how to sign-out from all your Gmail sessions.