should be, because:

- chrome/firefox/safari: has `MutationObserver`
- ie11: donno, but not released yet; if it has the `MutationObserver`, it'll use it
- ie10: no `MutationObserver` has mutation events via `addEventListener`
- ie9: no `MutationObserver`, has mutation events via `addEventListener`
- ie8: no `MutationObserver`, no mutation events (no `addEventListener` either)

iirc, the only UA which doesn't support (all) mutation events which has `addEventListener` enabled is chrome (they dropped `DOMAttrModified` some time ago).