Ask.com – Removing Other Search Engines from Firefox

Context Search

Search selected text using your preferred search engines. Right-click or Shift-click on selected text to respectively launch the context menu or the grid of icons. You can also perform searches using keywords in the url address bar.

The following addons appear to have since been deleted.

SearchWith (no longer avaliable)

SearchWith extension allows you to search selected with various search services. It adds a "Search With" sub menu on the context menu (right-click menu) with a configurable list of search services that can be used to search the highlighted text.

SmartSearch (no longer avaliable)

Right-click on a word or group of selected words, and from the popup menu, select a website. SmartSearch will perform a search as though you had gone to that website and entered the selected words. You may add any website to the menu by visiting that site, right-clicking on its search field, selecting "Add a Keyword for this Search..." and picking a name and keyword.

Ctrl+Up/Down arrow switches to next/previous search engine in the list.

If you want the search box to always go back to the default after a non-default search, install and customize the SearchLoad Options extension.

Alternatively, you may be looking for Second Search.

If you really want to be able to use a specific engine by typing its name, you want something like Obnibar or even Firefox's built-in keyword search feature. There are many other extensions for variations on keyword searching. Browse the Firefox Add-ons website.