Most of us don't own desktop computers anymore, laptops having become powerful enough to act as both portable and desktop PC. If you're regularly hooked up to an external monitor of significant size, vertical real estate isn't much of a problem.
Unplug, though, and vertical real estate is at a premium on most laptops. At one point, Google attempted to address the problem with a Chrome experiment that hid the navigation bar until you needed it. That feature was quickly done away with, though, and in fact never made it to the stable version of Chrome.
It didn't take long for the Firefox team to make the auto-hiding navbar feature available in Firefox in the form of an addon. The extension is developed by Mozilla itself as one of its Prospector experiments.
Once you download the addon (which doesn't require a restart) the navbar is simply hidden until you hover your mouse over it. The traditional keyboard shortcut (ctrl + L) to place the cursor in the address bar also brings it into focus.
If you want to keep the navbar in view, but still want that precious vertical real estate, you can opt for One-Liner, which combines the navbar and tabbar into a single toolbar.
Enjoy that sweet real estate.
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