[keeperofdakeys]

Firefox has "about:memory", which can give you some rather detailed information about memory usage.

[swatthatfly]

Chrome has chrome://memory-redirect/

[keeperofdakeys]

Strangely I can't find it in the latest dev release of chrome or chromium, it's still in stable. At least on linux, it also shows firefox's total memory usage, maybe they are doing lots of comparisons.