About button beside of logout button we get a popup window you can activate the developer mode.

Thanks! 

But the button before logout button is Help.

When clicking Help button sends me to:

https://doc.odoo.com/v6.0/book?version=6.0.4

There is no Enable Debug mode :(

i Eduardo,1) You can see a small button just before the logout button. Press it2) Click on "Activate the Developer Mode" link from the "About" Popup box..

Or 

Help > Enable Debug mode tooltips

It will switch to Developer World :)