"Mozilla-that-runs-in-more-than-one-thread sounds even nicer."
In mobile Firefox ("Fennec"), website processes already run in a different process than the main UI. For now, it's one process for all tabs, but that will be relatively easy to split to multiple ones in the future.
The focus is now to rework all the UI code in desktop Firefox (which has much more of that UI than Fennec) to support that process separation.
And of course, B2G will profit from all that as well.