Turn off beep sound in firefox
I recently installed new firefox version on my ubuntu and was trying to find some text on a webpage. Suddenly, as I pressed next to search it, the searchbox turns red showing Phrase not found and started making beep noise. I was annoyed, So was thinking of way to disable / turn it off. To look for some preference to set, I typed about:config (special firefox about: pages) in location bar and searched for sound. I was lucky i found two related preferences.
So you can set accessibility.typeaheadfind.enablesound Value to false by double clicking it. And you are done. No more beep beep to annoy you.