Any idea why the "slim" numbers are moving steadily in the wrong direction?
More generally, AWSY is useful for identifying some regressions, but it's one specific, unrealistic workload. You can't use it to judge Firefox's overall memory consumption.
For example, looking at AWSY you'd think Firefox 13 had the best memory consumption. But I guarantee you that Firefox 28 has better memory consumption. In particular, Firefox 28 has fewer bad cases where memory consumption spirals out of control, and those are the cases that really hurt performance and stability. Using 10 or 20% more memory at start-up, for example, isn't a big deal in comparison.
Problem is, this does not convince Average Joe about the slimness of Fx. I asked them to set up a main chart using only the stable ones with the latest changes (allocation), but it was ignored. IMHO that would help them see the what the end user would see over the long course, and A. Joe would see what actually effects him (as he is unlikely to use dev channels).
Edit: the charts also do not show the improvements in Garbage Collection (IGC in Fx16, upcoming ICC and GGC) and the memory management with add-os (Hueyfix in Fx15).