Short Answer

Bookmark the following URL:

chrome://browser/content/preferences/cookies.xul

Short-ish Answer

FireFox stores all of its UI elements in files called XUL files.  chrome:// URLs point to these various XUL files on your hard drive.  They live inside JAR files (Java ARchives), which are essentially zip files.  Chrome URLs beginning with chrome://browser will point specifically to a file called browser.jar, which lives in your Firefox installation directory.  On Windows 7, in my case, this was at C:\Program Files (x86)\Mozilla Firefox\chrome\browser.jar.

From there, the rest of the URL is pointing within the JAR file.  In this case, we’re looking at content/browser/preferences/cookies.xul, which is within browser.jar.

It’s that simple. When you point FireFox to a chrome URL, assuming it exists, it will be displayed. To see a useless but funny example of this, try this URL:

chrome://browser/content/browser.xul