What html editor do you use? Html is a very funky language and has limits and the same code can look different in many browsers. If you want HTML control you need to use a program like dreamweaver, this way you can get through some of the inconsistencies.
Try turning the caps lock on and forcing it to begin a new cycle by pushing the page-up(next frame) button and the caps lock will hender the rendering… It’s not instant but it should cut the frame render time some.