Just Type the url's written below in new tab and hit the enter, see the effect.
1. chrome://global/content/alerts/alert.xul
It SHOWS Dancing Firefox.
2. chrome://browser/content/browser.xul
It Opens another Firefox inside a tab in the the existing Firefox window.
3. chrome://browser/content/preferences/preferences.xul
It Opens the Options dialog box inside the Firefox tab.
4. chrome://browser/content/bookmarks/bookmarksPanel.xul
It Opens the “Book Marks Manager” inside a tab in the Firefox window.
5. chrome://browser/content/history/history-panel.xul
It Opens the History Panel in the Firefox tab.
6. chrome://browser/content/preferences/cookies.xul
It Opens the “cookies window” inside a tab in the Firefox window.
7. chrome://browser/content/preferences/sanitize.xul
It Opens the “Clear Private Data” window inside the current tab.
8. chrome://browser/content/aboutDialog.xul
It Opens the “About Firefox” Dialog box inside the tab.
9. chrome://browser/content/credits.xhtml
It A scrolling list of names. The one’s who we must thank for creating Firefox