Here's my estimate:
* A dozen build engineers to support development and builds for X client platforms
* A dozen engineers for the Javascript VM
* Dozens of engineers to support ongoing javascript and CSS standards
* A dozen engineers or more to support the firefox core
* Dedicated teams for Android, MacOS, Windows and Linux targets
* Dozens of Team/Programme/Project managers to _enable_ devs to do their best. These folks aren't optional.
* UX designers
* Graphical design artists
* Technical writers