As a chrome extension developer I really like this. Previously I didn't develop extensions for other browsers because I would have to learn another ecosystem. Now it could be pretty simple to do.

I also like that all of the asynchronous API calls are returning Promises. Chrome API is still using callbacks. This also means that some time will pass while this is even added to chrome. I expect that there will be a polyfill library that translates the new API calls to legacy browser API calls.