Here’s how to disable the new search bar:
1. Go into the config by typing the following in the address bar and then hitting return (click “I’ll be careful, I promise!” if a dialogue comes up mentioning anything about dragons, if not just continue):
2. Paste the following in the wide “Search”-field that appears:
3. The value should be “true” by default, double-click on it so it says “false”
4. Restart firefox, the search bar should now have gone back to normal.
Hope that helps.