For Firefox, open FF, click on "Tools", then on Add-ons, or Extensions. Find the Yahoo Toolbar listing and click on it, Select Uninstall, choose "yes/OK", when it asks: "Are you sure?".
For Internet Explorer, see the link below. (Uninstall it from the "Pencil" icon in the toolbar itself.):
Hope this helps.
I cannot find Yahoo Toolbar in the Control Panel - Programs and Features.
How can I remove/delete Yahoo Toolbar?