The Chrome browser project, codenamed Chromium, has released documentation on its upcoming Extensions mechanism. There’s discussion of the project statement, the seven goals of the extension system (Webby, Rich, General, Maintainable, Stable, Secure, Open), and common use cases prior to disclosing their current proposal. Here’s the top-line proposal:
We should start by building the infrastructure for an extension system that can support different types of extensibility. The system should be able to support an open-ended list of APIs over time, such as toolbars, sidebars, content scripts (for Greasemonkey-like functionality), and content filtering (for parental filters, malware filters, or adblock-like functionality). Some APIs will require privileges that must be granted, such as “access to the history database” or “access to mail.google.com”.
Extension components will typically be implemented using web technologies like HTML, JavaScript and CSS with a few extra extension APIs that we design. Extensions will run in their own origin, separate from any web content, and will run in their own process (with the exception of content scripts, which must run in the same process as the web page they are modifying). Some form of native code components may also be supported, but the goal is to minimize the need for this in extensions.
Read the full proposal and follow the project at dev.chromium.org.