Normally, I am quite happy with Omnibar, thus, the high rating.
However, a bug patch landing in the April 19, 2014 Nightly broke the search vs. select a link from the dropdown list functionality in the URL bar. When I type a keyword in the URL and then go to select a bookmark that shows in the dropdown list, I get a search on the keyword when I should be having the bookmark open instead. When I disable Omnibar, the link I click on opens as expected.
I do not see anything obvious show up in the browser console or error console.
Edited to add: I just tried in a profile with only Omnibar installed and the issue persists.