Changes

This is the default tool for looking at memory usage. One approach to finding targets for memory reduction is to look at the about:memory report for a small content process (for instance, example.com) and see what is using up memory. In addition to using it to guide memory reduction work, we can work to reduce the heap-unclassified number (memory allocated by Firefox but not reported in about:memory) in tests of interest. Adding new reporters often leads to finding things to improve. === DMD ===[https://developer.mozilla.org/en-US/docs/Mozilla/Performance/DMD DMD] (aka the Dark Matter Detector) complements about:memory. When DMD mode is enabled, Firefox tracks the address and allocation stacks of all live blocks of memory and can save that information to a log for offline analysis by dmd.py. The primary use is investigating heap-unclassified, but with alternate modes enabled it can be used for other tasks like investigating leaks.