The Are We Slim Yet project (commonly known as AWSY) historically has tracked memory usage across builds on the website areweslimyet.com. It uses the same infrastructure as about:memory to measure memory usage on a predefined snapshot of Alexa top 100 pages known as tp5. More details can be found in the AWSY FAQ. Large regressions are flagged by filing a bug in bugzilla.
As Firefox transitions to using multiple processes by default, we are working on moving AWSY into the TaskCluster infrastructure. This will allow us to run measurements on all branches and platforms. The results are posted to perfherder where we can track regressions automatically.
As new processes are added we want to make sure their memory usage is also tracked by AWSY. To this end we ask for memory reporting to be integrated into the new process before it is enabled on Nightly.