debian: mozilla into cgroup limiting memory?

`ulimit -v` doesn't work very well for multithreaded applications to limit their memory usage because it just spawns off more processes when it wants to hog more resources, and any limit I've found to stop it crashing my machine are unrealistically small per process and stops legit tabs from running. How, as an unprivledged user on debian, do I put mozilla into its own cgroup limiting its memory usage to ~ 50% of real memory (16GB ought be enough for 3 tabs these days, eh?). -- Tim Connors