NOTE: This answer was provided prior to it being known that the question was about Firefox 3.6.13 (mentioned for the first time in the comments to this answer). After that comment was made, I edited the question and title to include that significant piece of information. This answer has been left here in case someone looking for the information for current versions of Firefox happens to land on this page as the result of a search.
For the last few/several versions of Firefox (from Firefox 29.0), the "Title Bar" has been hidden by default.
You can hide/unhide the "Title Bar" from the customization dialog which can be reached by clicking on the icon on the far right of the toolbar containing the urlbar. This icon, by default, looks like 3 horizontal lines. You will then need to click "Customize" (bottom left of popup). The button to display/hide the "Title Bar" is on the bottom left of the window which will be displayed within the browser upon hitting customize.
You can also directly change the option to show the "Title Bar". In about:config
(enter about:config
in the urlbar) you can change the state of browser.tabs.drawInTitlebar
.