add 'more info' to extension listings (both html and css)

Let me know if the format/conditionals are okay, or if you want to check that a homepage exists in the .json files through the .js files.
Yes, that's right - they're two different things. Think of it as two layers of encoding. Entity-encoding is for the text content of an HTML file, regardless of whether it's a URL or not. URL-encoding is for URLs generally (regardless of whether they're in HTML). Attribute values in HTML are always supposed to be entity-encoded - that's what prevents XSS (since it encodes `&`, `<`, `'`, and `"` using the &-entity forms). So it's correct to have, say, `<a href="http://foo.com?blah=1&amp;foo=2">` - the `&amp;` will be decoded by the HTML parser into a plain `&` before it ever gets used as a URL.