Where do you see Yahoo as the search engine?

Is that with searching via the location bar or the search bar on the Navigation Toolbar ?

Try to reset some preferences to the default with the SearchReset extension:

• https://addons.mozilla.org/firefox/addon/searchreset/

Note that the SearchReset extension only runs once and then uninstalls automatically, so it won't show on the "Firefox > Add-ons" page (about:addons).

If you do not keep changes after a restart then see:

• http://kb.mozillazine.org/Preferences_not_saved

If there is a problem with searching via the default about:home page then try to reset the search engine used on the about:home page.

Reset the browser.startup.homepage_override.mstone pref via the right-click context menu to the default on the about:config page and close and restart Firefox to restore the about:home page to its default.

• http://kb.mozillazine.org/about:config

1. Open the about:config page via the location bar
2. Type in the Filter bar: mstone
3. Right-click the browser.startup.homepage_override.mstone line and select: Reset
4. Close and restart Firefox

If this didn't help then delete the delete the chromeappsstore.sqlite file in the Firefox Profile Folder and repeat the above.

I had to remove the anti-phising software Domain Adviser to stop navigation bar search from redirecting to Yahoo search.

about:config and downloading DEVONtechnologies EasyFind to destroy the hidden Yahoo files in the Library on a Mac no longer works. I suspect Yahoo has found a way to undermine those fixes. It is infuriating to find that a responsible operator such as Yahoo needs to stoop to this to find users to its dying web browser. Are there any other suggestions? Many thanks