We have members of the devtools team in our San Francisco, London, Vancouver, Paris, Toronto, and Portland offices, but many also work remotely.
Some of the things we're working on:
A performance tool that incorporates a sampling CPU-profiler, platform events tracing, and information from SpiderMonkey's Just-In-Time compiler
An allocations and heap usage profiler (this is what I'm working on, and I wrote about it here)
A WebGL shader live-editor, and a canvas debugger to step through individual draw calls
One of the most important things for me is that every line of code we write at Mozilla is Free and Open Source from day one, and we're dedicated to keeping the web open.