How to Uninstall Yahoo Toolbar From Firefox
Many software companies have partnerships with Yahoo!, which means that they receive a small stipend to distribute the Yahoo! browser toolbar with their software. Thus the Yahoo! toolbar may be a default installation option in some programs, i.e. it's installed on your computer even if you have not requested it. Uninstall the Yahoo! toolbar from Firefox if it has been automatically installed or if you no longer want it.
Launch Firefox. Click the "Tools" menu at the top of the screen, then click "Add-ons." The "Extensions" tab should already be selected. If it is not, click it.
Click the entry for the Yahoo! toolbar, then click the "Uninstall" button to remove it from your system.
Click "Yes" when prompted to confirm that you want to remove the Yahoo! toolbar from Firefox.
Click the "Restart Firefox" button after the removal is complete. When Firefox restarts, the Yahoo! toolbar will no longer be displayed.