Debugger.Memory - Firefox Developer Tools
you can retrieve the current log by calling dbg.memory.drainallocationslog.
... allocationslogoverflowed returns true if there have been more than [maxallocationsloglength][#max-alloc-log] allocations since the last time [drainallocationslog][#drain-alloc-log] was called and some data has been lost.

Handling common HTML and CSS problems - Learn web development
it is really easy and convenient to use, although it does have some downsides (see the link above for details), and it is arguable that parsing every stylesheet in your site and add prefixes at run time can be a drain on the computer's processing power for a large site.

Power profiling overview
a cruder technique that works with mobile machines and devices is to run a program for a long time and simply time how long it takes for the battery to drain.

Shell global objects
drainjobqueue() take jobs from the shell's job queue in fifo order and run them until the queue is empty.

Tutorial: Show Allocations Per Call Path - Firefox Developer Tools
var log = dbg.memory.drainallocationslog(); // neutralize the debugger, and drop it on the floor // for the gc to collect.

Battery Status API - Web APIs
this can be used to adjust your app's resource usage to reduce battery drain when the battery is low, or to save changes before the battery runs out in order to prevent data loss.

Index - Web APIs
this can be used to adjust your app's resource usage to reduce battery drain when the battery is low, or to save changes before the battery runs out in order to prevent data loss.