> I get an error message: "Firefox could not install the search plugin from because an engine with the same name already exists."

Can you give an example of a site you are trying to install from?

By default, Firefox will have a conflict with built-in search engines like Google, Bing, DuckDuckGo, Amazon, eBay and Wikipedia. (In various parts of the world, that list might include Baidu, Yandex, or others.)

> When I go to Preferences < Search and then click the "find more search engines" link, I can find them and download them, but they don't show up as an option in "Search Shortcuts."

When you add search engines from the Mozilla Add-ons site (using the blue "Add to Firefox" button), they should also appear on the Add-ons page as extensions. If you check that list, are they successfully installed and enabled? You can access it using:

• Command+Shift+a (Windows: Ctrl+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• type or paste about:addons in the address bar and press Enter/Return

In the left column of the Add-ons page, click Extensions. On the right side, find the "Manage Your Extensions" heading.

Are your add-on search engines showing up here?

If you can't make an installed search engine show in "Settings -> Search" then try to add a keyword that starts with an '@'.

> When you add search engines from the Mozilla Add-ons site (using the blue "Add to Firefox" button), they should also appear on the Add-ons page as extensions. If you check that list, are they successfully installed and enabled? You can access it using:

Ahh, yes, this is helpful. I do see the add-ons there, under Preferences> Extensions. I was trying to add merriam-webster thesaurus as a search, and it didn't show up as one of the options in my search bar at the top right, so I was confused. Now I realize that the way it's meant to work is to highlight and right click a word and then search from a new window. I'd still rather have it as a search engine option but I think I understand what's going on now.