To play just a bit of devil’s advocate on this one…
Regardless of how a page looks in edit mode, it’s very likely it will look different in all of the browsers. For example, I position a text box in edit mode and it is in the same position in Run Mode.
However, the second I preview in browser, it all falls apart. It’s different in IE, Chrome, Firefox, etc. I’ve attached a typical display for each one. The Run image represents where the text box is in the title editor. Not one of the browsers match the location. Notice that Chrome has the box higher than the Run, then Firefox and IE have near identical locations.
It does totally stink that there are differences, especially in browser preview, that there are so many differences. It means I have to tell my learners that the courses are designed for IE, but there may be differences in appearance across different browsers.