The record of search history which appears in the search box on Yahoo! is actually a feature controlled by your browser, not Yahoo!
You may stop the search history from being generated in the search box by following the instructions below:
Internet Explorer users:
From here you can click the "Clear Forms" box to delete your current history, or you can uncheck the Forms box to permanently stop the generation of the search history.
Mozilla Firefox and Netscape users:
This will remove the stored searches as well as prevent the storage of new search terms.
Safari browser users:
To disable the AutoFill feature on Safari, click on "Preferences" from the Safari menu, then unclick the "AutoFill" button.
Yahoo! Toolbar Search History
There are several ways you can clear the search history in your Yahoo! Toolbar. Depending on what version of Toolbar you are using, to access this setting you will either click the pencil icon or the "Settings" tab in your toolbar.
If you want to remove all the entries in your toolbar search history right now, but you still want Yahoo! Toolbar to remember your searches in the future, do the following:
If you want to save your recent searches while you're searching on the Web, but automatically clear the saved searches when you close your browser window, do the following:
If you want to disable the feature in Toolbar entirely so none of your searches are saved, do the following:
Note: Yahoo! Toolbar for Mozilla Firefox currently does not have the ability to disable the search history or automatically clear it on exit. Those features will be added in a future release.
If you've disabled the search history in Yahoo! Toolbar but are still seeing items suggested when you type, your browser is saving that information. For Internet Explorer, check your options under Tools > Internet Options > AutoFill. For Mozilla Firefox, check Tools > Options > Privacy > Saved Form Information.