Rated 2 out of 5 stars

Great for older Firefox versions. For those looking to replace it, I suggest Beyond Australis. On the options for that add-on, you can activate the Awesome Bar and check "show search engines in the location bar." It will give a similar feel to Omnibar. If you do not want the bar to auto-hide, under the slim chrome panel on the left, you can also uncheck "also hide navigation bar".