If you have the Chrome web browser installed (by Google, see google.com/chrome), try typing this into the address/search bar:
and press ENTER, you will get a page displaying browser memory information..
“About memory | Measuring memory usage in a multi-process browser.”
It gives you a “summary of memory used by currently active browsers”. So if you have Firefox and Internet Explorer (and Opera and Safari) open at the time you type that command, it shows you memory information for those browsers as well. And it details how much memory is being used by the different tabs.
See the above screen capture.