Since we are going to start backing people out for breaking ggc soon, it will be desirable if their local builds reflected this configuration. On the other hand, we don't want to perturb performance work targeting the browser. Luke suggested a satisfactory compromise: flip the default only for debug.
People who want GGC perf wins are keen to follow the right bug. Which one is it? Not this one, if this one will be resolved fixed when GGC is on only for debug builds. /be
Bug 875863 is the meta for ggc perf.
We ended up not needing this.