What happens when you restore default search? see screenshot

You can also get it here. https://addons.mozilla.org/en-US/firefox/search/?q=yahoo&type=extension

on Default setting there is simply no Yahoo search engine

Thanks, I was able to add Yahoo search to Fairefox. Also, when I click on search engines there is no DELETE button

I see remove. see screenshot If there are no more questions mark it as resolved and have nice day.

how to add Yahoo search as default search engine if Yahoo is missing on Firefox Search. on Search setting i can see different engines Google, Bing, Ebay, etc. but there is no Yahoo.

Yahoo was removed as from being one of the search engine defaults for a long time now since Firefox 57.0 and on. https://support.mozilla.org/en-US/forums/contributors/712925

You have to add Yahoo as a search engine if you want it in Firefox. https://support.mozilla.org/en-US/kb/add-or-remove-search-engine-firefox https://support.mozilla.org/en-US/kb/add-custom-search-engine-firefox https://support.mozilla.org/en-US/kb/change-your-default-search-settings-firefox