Volume Mixer in Windows 7, not just show device volume but also lists all applications that are currently running and producing the audio. You can control the audio of any of the application from there on. So when you are having more than one application that is producing sound you can control from here and stop it as well.
For enabling and disabling JavaScript you need an add-on for SeaMonkey called quick java . You can download this free add-on from mozdev.org or just Google for it. After installation you will be able to see two buttons near the progress bar, for enabling and disabling JavaScript and java. Just click on the buttons to disable and enable JavaScript or java. There will be separate buttons for java and JavaScript.