Chrome's ability to temporarily edit and save changes to JS sources through the debugger editor is fantastic though.
Other than that it's mostly just improvements to what FF already has.
Search could be made much more useful, especially network requests. Searching all request bodies/responses for a particular string/json/regex would be a huge step up.
You can search the response of individual requests but there's a UI bug that makes it look like your filter is no longer applied when you select the next one in the list.