You can no longer revert back to old Search bar interface in Firefox. With Firefox 34, Mozilla introduced a new search interface or so called one click searches UI, for which, underneath the search suggestions for your search term, you’ll see an array of search engine buttons.
These buttons allow user to find a search term directly on a specific site quickly and easily. Till now, Mozilla allowed to disable one click Searches UI in Firefox browser through an about:config preference browser.search.showOneOffButtons, now the old search UI, its code and the preference have been fully removed from Nigthly, which is at version 43.
Make Firefox’s New Search UI look similar to the old Search bar UI
So Firefox 43 will miss oneoffbuttons preference. The new Search UI is here to stay, so get used to it or make it more like to the old one, here is how.
1. Click on Menu > Options > Search
2. Under ‘One-click Search engines’, keep the default search engine ticked, and uncheck all other search engines, now the Search bar looks like this when you type a search term