innerHTML updates layout every time it is read. This can be seen on "http://celtickane.com/projects/jsspeed2007.php", where on the DOM test (actually primarily a test of innerHTML) we are currently the slowest of any browser.
Created attachment 16467 [details] don't update layout for innerHTML
Comment on attachment 16467 [details] don't update layout for innerHTML I also looked, it appears that createMarkup(Node*... does not actually touch the render tree (renderer()) so I agree, this looks safe. r=me
Incidentally this patch is a 65% speedup on that one test in the benchmark.