One of the handiest features in Firefox, and one that I use frequently and absent-mindedly, is the “find as you type” shortcut. Press forward slash, and Firefox will jump to the next text that matches what you type; press single-quote, and Firefox will jump to the next link text that matches what you type. So fast and invaluable.
Unfortunately, if the string you type turns up no results, Firefox alerts you with what sounds like “a hoarse dog barking.” Not just once, but for every subsequent character that confirms your search failure: a curse for fast typists.
After not trying very hard to find a solution via Google, I thought “what the hell” and went to about:config. Searched for “sound,” and voilÃ . “accessibility.typeaheadfind.enablesound”. Double-click once, restart Firefox, and no longer will you be plagued by the hoarse dog.