Worth checking out here http://www.paessler.com/psi/download
Supports Internet Explorer/Mozilla based browsers (including Maxthon etc). Allows you to inspect all sorts of information about websites visited (including CSS sheets etc.) and comes with lots of plugins built in.
They are not always quick to update Firefox plugins but I have checked and 188.8.131.52 is supported.
It comes with its own 'Analyzing Browser' which looks like this:
But also has toolbars for IE and Firefox and right click context menus.
Here is an example of the sort of analysis output it provides: