It could be a good thing to have the option to have tabs that displays different previews.
Per example, im coding some specific php page and i like to see it, but could be nice to have some additional tabs to see other pages that are affected by the one im coding. Per example the homepage of the site, to see if the submenu displays me page well, etc.
In coded websites its very common that some change in one single php affects more than one page and it could be nice to be able to display them all and change it with a tab.
I hope i make my point
(I have more suggestions, just will be posting them whenever im sure about them)
Thanks in advance.