It's hopeless. Because the JavaScript code must be sent to the browser in order to run, you can't prevent sophisticated users from seeing it.

Firebug isn't even necessary: the page source can be viewed by pressing Ctrl+u and if the JavaScript is in a separate file, clicking the link to the file in the <script> tag will display it. When you add the script dynamically, it still can be viewed using the Web Developer extension or the DOM Inspector extension. The file probably is in the cache as well.

Many people "minify" their script code, which makes it extremely difficult to read. However, some people still can make sense of it. (I'm not one of them.)

What's so important to hide, anyway?

Yes, it's very important to hide it.

I did some settins in .htaccess so if someone trying to access script by using the path nothing is displaying. Also this method doesn't show the content inside <script...>" and "</script>" when you viewing the page source (except Firebug).

Cache is denied by http-headers.

I already thought about the last one you wrote about. I'l try to minify the code later, but now I want to protect it in other availible ways. Really, very bulky stuf and it needs more protection.

About the extention (how to block). Founded this article but there is no such property (at least in last version of Firebug) window.console.firebug = undefined.