The big big difference between the platforms is that extensions are sandboxed on Chrome. I'm convinced that this is the only way to go. Free-reign extensions inevitably lead to instability and support is a nightmare because you can never be certain of what is going on in your own app.<p>However, the sandboxing is severely limiting. Extensions get a separate JS environment for each tab and they can only communicate through async messaging. This makes global state, like user settings, a pain in the arse. I think they can do better than this while remaining secure.<p>And of course, you can only extend the browser using the specific hooks it provides, which currently doesn't include much in the way of user interface modification. I'm sure that more hooks will be provided in the future.<p>They did a great job of keeping it simple though. Nearly everything is done through standard JS/HTML/DOM. XPCOM will not be missed.<p>And now for the plug, though it might not work yet:
<a href="https://chrome.google.com/extensions/detail/ljecomdaijmibecakcpjadigpfkollbh" rel="nofollow">https://chrome.google.com/extensions/detail/ljecomdaijmibeca...</a>