Also for firefox, check out the web developer extension,
https://addons.mozilla.org/en-US/firefox/addon/60. It has all kinds of useful info for design and testing of pages.
For example, to show all elements go to "information > display element information". It will outline all elements on the page and show you their attributes, css ancestors and css children. You can do the same for all the css selectors by choosing "information > id & class details".
If you're using 4.1.6, in webmaster mode, if you hover over a .tpl file in the pop-up window, a border will appear around the area of the page affected by that .tpl file.
regards,
n00bert