How do I hide the code of my theme? Is it possible to hide the code of the theme that I have created for my client? In other words, when I open the page with firebug I dont want to see the HTML and all the CSS of my theme, also when I click with the right mouse button.
No, the browser needs to download the markup and stylesheet to do its job, and you shouldn't try this kind of thing, It doesn't work and is annoying to site visitors. 

Please read the answers on this similar StackOverflow question: https://stackoverflow.com/questions/6597224/how-to-hide-html-source