Rated 5 out of 5 stars
This is my summary about this add-on after using it intensely for more than a year:
It is also the only solution that also allows full control over WHEN to disable JS. The very moment you notice annoying activities on a website (ex. lots of animation, overlays popping up, etc.), you just click the red JS icon and they stop. But it's your call, always...
... because thankfully, this add-on does not assume by default you don't want JS (like NoScript does). That would be an absolutely inadequate assumption for contemporary Internet. (In times of Ajax, most websites are tuned to work *with* JS, not without. Amazon? Google? They all need JS for their full feature sets.)
LBNL, it is extremely light on resources. With only 8.2K, it's a flyweight among its fat "colleagues". (NoScipt is 500+K, for ex.)
And yes: It doesn't run "in the background", so it doesn't slow down Firefox at all.
There are absolutely NO privacy and security risks with this add-on (despite someone's lame attempt to suggest so in the comments below.)
All in all, JS Switch is a jewel in simplicity and elegance. It does ONE THING, and IT DOES IT WELL. Just the way software should be. Many thanks to the developer! Great work!
Now a few words on those negative ratings below:
Both ratings and comments are absolutely unjustified and out of place!
The rating system is not meant to express personal preference, but to rate if and how well an add-on works as advertised. Obviously, whether color is used to indicate status is a matter of personal taste. I have found color for status visualization an excellent choice, but moreover, the add-on description doesn't falsely suggest otherwise.
The other one... Well, that other rating looks like it is by someone affiliated with NoScript. If so, that's so lousy that I don't even have words for it... But even if not, rating and add-on poorly because they *prefer* another one - that's just ridiculous.