Firefox lets you define own keywords: abbreviations to use as a URL shortcut for a particular search engine. If you have defined ws as a keyword for the Wikipedia search for example, you can type ws SEARCHTERM into the location bar to search Wikipedia for SEARCHTERM.
To assign a shortcut for a search engine from the search bar, click the icon to the left of the search bar and select Change Search Settings. Select a search engine, double-click its Keyword column, enter a keyword and press Enter.
It is also possible to define a keyword for any search field on a Web site. Proceed as follows:
Right-click the search field and choose Add a Keyword for this Search from the menu that opens. The Add Bookmark dialog appears.
In Name, enter a descriptive name for this keyword.
Enter your Keyword for this search.
Save this keyword.
Tip: Keywords for Regular Web Sites
Using keywords is not restricted to search engines. You can also add a keyword to a bookmark (via the bookmark's properties).