Many search engines (including Yahoo, Google, Bing and others) provide search suggestions, which are based on popular searches other people make that are related to a word or words that you enter. When search suggestions are enabled, the text you type in a search field is sent to the search engine, which analyzes the words and displays a list of related searches.
If you see a search suggestion that matches what you are looking for, click on it to see results for that search term. This can save time and help you find what you’re looking for with less typing.
Enabling search suggestions will send the keywords you type in a search field to the default search engine - unless you appear to be typing a URL or hostname. Search fields include:
Search suggestions can be enabled or disabled at any time by checking or un-checking the Provide search suggestions box in the Search section of Firefox's optionspreferences: