To remove the yahoo toolbar (or any other toolbars you encounter) go to tools => add-ons => extensions, search for the yahoo toolbar and click remove. Follow this link for a longer step by step answer: Step by step guide on removing the yahoo toolbar

I followed the steps but saw no Yahoo toolbars or references to remove. Is this the same procedure to resolve the Yahoo-browser-search-interference problem i'm having ? (i use a Mac) thanks

Sorry, I misunderstood your question, I was kinda in a hurry when posting that. To get google search back, all you have to do is click on the small array next to the yahoo logo in the small search bar and select 'Google'. To remove yahoo-search right click 'Yahoo' and select remove.

Hopefully this will solve your problem.