In Firefox when you start typing the web site address, it tries to list down the web sites or bookmarks containing those characters. This is basically retrieved from history and Firefox bookmarks. You can prevent Firefox from suggesting history and bookmarks in Location bar by using the Firefox options menu.
Click on Tools –> Options –> Privacy tab
Under Location Bar, click on the When using the location bar, suggest dropdown and set it to Nothing. The other list of options available under this drop down are