I hope this is as easy as someone writing an extension that restores the functionality. Maybe this can spur some innovation for Firefox users via extensions.
Extensions can add address bar suggestions, but not a new search bar. It's unclear if Mozilla intends to remove that as well, I haven't seen any webextensions that add a search provider to it.
There are several extensions that use userscripts, like Greasemonkey and Tampermoney, so loading the search manifest files shouldn't be a problem.
