Ok, I've implemented such a feature--but keep in mind it's a bit rough in some areas. You can search a URL and view the results either as source or see the changes/highlights within the page itself. Excluding html tags from the query would, however, take a great deal of work than I care to do, so don't be surprised with the occasional format breakage on a page. Also, at present, it won't elegantly integrate an intricately designed website with the find highlighters -- so there's plenty of breakage there. But there shouldn't be too many complications with the replacement aspect--much simpler than the find/preview functions!