See also #1884.

Greasemonkey has special support for the "userscripts.org" domain and will check for updates via their "meta.js" convention, rather than downloading the whole script.

This mechanism could be extended to work across the whole internet. I'm imagining some sort of:

1. Check for update, first time at meta.js. If we failed to find meta.js before, use normal download location.
2. If found, just use it as normal, done.
3. If (meta.js is) not found, record that fact and restart the process.
4. If an update is found no matter what, reset the "meta.js found/not found" bit. To give authors a chance to add it later, i.e. if a script suddenly becomes popular.