Firefox doesn’t currently bounce the Downloads box in the dock when a download is finished, like Safari, Chrome and Camino do.
If Firefox was written in Objective C, you could very easily add the one line of Objective C code required to do this. However, it’s not. Is there a way to call this Cocoa function from C++ so that it can be added to Firefox for the benefit of all Mac users?
You can use the Carbon API’s CFNotificationCenterPostNotification.
Carbon is pure C.
Documentation and code samples here.