If the bottom bar is only missing when you're using your web browser, it means that you're using full screen mode. As Minnuasheeka states, you can toggle between the normal display and full screen display by pressing F11.
However, if the bar is missing when the desktop is displayed it's likely that it's still there but with zero height. Move the mouse cursor to the bottom of the screen and it should switch to a vertical, double-ended arrow. That shows that it's resting on top of the bar. Hold the left mouse button down while dragging the top of the bar up to its usual position.
Chris