From MozillaZine Knowledge Base
Find As You Type (or Type Ahead Find as it was originally called) allows you to start finding text on the page immediately by simply typing the text you’re trying to find. When typed characters fail to match anything on the page, it can be configured to play an alert sound. This sound can be a built-in sound, a system beep, or an external user-specified file.
Possible values and their effects
The default, built-in sound will be played on failed matches. (Once described as “a hoarse dog barking.”) (Default in all products; default in Firefox until 2.0)
The system beep will be played on failed matches. (Default in Firefox 2.0)
(valid path to a WAV file)
The WAV file will be played for the alert sound on failed matches.
No sound will be played (equivalent of setting accessibility.typeaheadfind.enablesound to false).
First checked in
Has an effect in