Hi heger.kyle, you can install a Yahoo search plugin and make that your default search engine. Then when you search from the address bar or the search box built-in to Firefox's Home/new tab page, the results will appear on Yahoo. Here's how:

(1) When you are on Yahoo, for example, https://www.yahoo.com/ , click the Page Actions menu button in the address bar (•••) and use the command at the bottom -- Add Search Engine -- to install the Yahoo search plugin. Now Yahoo should appear in the "one click" buttons when you are using a built-in search feature.

Does that work?

(2) Then you can switch your default search engine to Yahoo using the steps in this article: Change your default search settings in Firefox.

Does that solve it or are there other things you would like to change, too?

When I selected the link "Change your default search settings in Firefox," and play the embedded video, I'm told to select the "menu" icon at top right of page, which I do. Then, I'm told that I'll find an option called "preferences," but I don't.

What should I do now in order to change my default search engine to Yahoo.?

On Windows, you need to look for "Options" in the "3-bar" Firefox menu button drop-down list (Preferences is used on other platforms).

Hmm, on Windows it is called Options and on Mac and Linux it is called Preferences. This site usually can properly detect your OS so it's strange that it didn't work for you.

By the way, here's another method:

Start typing in Firefox's Address bar or in the Search box on Firefox's built-in new tab page. On the suggestions drop-down, you should see the Yahoo search icon after the others. Right-click that icon, then click Set As Default Search Engine.