Does the job, but I'm not a fan of the yellow icon.

Good. As others have said would be better if you could toggle the default behaviour.

A nice simple add-on that does exactly what I want, which is block Javascript based on the site by default, but it allows me to turn it on for any site with a simple click. And it works in Firefox 57, which is nice, because at the time of writing, NoScript doesn't support Firefox 57.

The default Javascript state is off for this extension, one click to enable it for the site/page (?) - and it remembers. This is exactly what I was looking for.
If you like it the the other way around, try "NJS" or "Quick JS switcher".
This gives me exactly what I want.

The ''default policy'' IS correct. Having it in reverse is a security risk, nullifies using the addon in first place and makes it pointless.

"so that users may choose to block nothing until they encounter a problem site (and then block JS if they want)."
- and by then it would be too late. My comment was spot on and needed to stop the useless spamming. The addon you want is noscript (or none at all).

Great idea, well executed, just not convenient for many users. It would be much easier (as many have already said) if the extension was configurable so that users may choose to block nothing until they encounter a problem site (and then block JS if they want).

So I will be uninstalling this and installing Quick JS Switcher instead. Just use the search box to find it.

The hostile comment by anonymous was not a helpful contribution. People can have different ideas to you. It is allowed. :-)

I really liked this add-on apart from its default policy, so I forked the Code and edited to change the default policy, and made a new extension https://addons.mozilla.org/en-US/firefox/addon/quick-js-switcher/ , feel free to install that.

Most sites need JS to operate, and allow each site separately will only make it difficult to browse, can you add the option that the default will be enableing JS?