Chrome extensions already are open source (so to speak). They're simply .zip bundles, which run HTML, CSS and JS in the context of the page/browser [0]. The location depends on OS, but its pretty easy to find [1].

[0] https://developer.chrome.com/extensions/overview

[1] http://stackoverflow.com/a/14544700/2078412

That's not enough, as the behavior can be updated by Chrome to a new version without noticing me the user.

Yeah, we probably will. We seem to be getting enough installs already to justify putting more dev cycles in. :-)