To turn on inline autocomplete in the Firefox web browser...

1. Enter about :config in the URL field
2. Right-click on the page and create a new Boolean value
3. Enter browser.urlbar.autoFill as the preference name (note, case-sensitive: 'F', not 'f')
4. Set the value to true


To only matched typed URL's:

1. Enter about :config in the URL field
2. Find browser.urlbar.matchOnlyTyped or create it as a new Boolean value
3. Set the value to true