I'm guessing the reason you don't want to upgrade is because the new worse search bar that was included in Firefox 34? You can install a new version of Firefox and use Classic theme restorer[0] to get both the old UI and the new features. At least until Firefox 57 ships in November which will only support web extensions. It will be sorely missed.

[0] https://addons.mozilla.org/en-US/firefox/addon/classicthemer...