We're just getting started with WebExtensions, and have begun with a set of APIs that are commonly used with Chrome so people can kick the tires. We don't want to be a Chrome copy, and want to ensure we differentiate while integrating Electrolysis and other initatives into Firefox. To innovate will require input and assistance from the community, which we are actively seeking. The path for WebExtensions will evolve in the coming weeks, months, and years, and we want the developer community to be a big part of that evolution.
=== Are malicious addons really a problem? ===
Yes. Please read [https://blog.mozilla.org/addons/2015/04/15/the-case-for-extension-signing/ "The Case for Extension Signing"].