One possible culprit would be a Yahoo! extension. You can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. While you're viewing any page in Firefox, either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• type or paste about:addons in the address bar and press Enter/Return

In the left column of the Add-ons page, click Extensions. Then cast a critical eye over the list on the right side. Any extensions that Firefox installs on its own are hidden from this page, so everything listed here is your choice (and your responsibility) to manage. Anything suspicious? If in doubt, disable.

Often a link will appear above at least one disabled extension to restart Firefox before the change takes effect. You can complete your work on the tab and click one of the links as the last step.

Once you regain control of your Firefox from any add-on interference, you can change your home page on the Options page. More info: How to set the home page.

Thank you so much for your expertise. it was very frustrating and you made an old man happy