Об этом дополнении
Plugins like NoScript exists, I'm well aware. But these plugins are the cause of extra RAM and CPU load. ON/OFF switch is everything the user needs often, no local whitelists/blacklists, just one 16x16 pixels button on status bar for the ones who happen to like it. It does not have any preferences by itself, only global "javascript.enabled" key.
I'm on such an abomination of machine right now, even going Edit -> Preferences -> Advanced -> Scripts and Plugins takes a few minutes if not more. So an instant button really spares me a lot of time. Plus I'm in love with SeaMonkey status bar, adding such a button seems like an alright idea.