Sound notification of email receipt is not very useful to people who receive lots of non-urgent emails. Turn it off, and instead add this new filter action that plays a selected sound for each class of email that you receive.
SeaMonkey 2.0a2 and later, Thunderbird 3.0b1 and later
This version changes nothing other than to update the claimed compatibility range to current Thunderbird and SeaMonkey releases. Some users were complaining of getting "Addon is incompatible" messages even though AMO compatibility included their version.