I would really like to see something similar in Chrome.
If Firefox can keep the speed in improving UX, stability (looks they're overcame most random crashes from 4-9 times), responsiveness, memory usage, and even out-of-the-box toolset, then I suspect they will soon start seeing old users that left around 3.6 -> 4 transition (usually switching to snappier Chrome/Chromium).
I'm mostly used to Chrome by now (IIRC started using it around version 3), but somehow I still miss full-fledged add-ons, that allowed me to truly customize and enhance Firefox.
I mean enhance w/o some hackish workarounds that are needed in Chrome's extensions. Even ability to add global keyboard shortcuts  is still not present in Chrome. The thing is that you have to use content scripts much more often than they should be needed. It is bad if you have dozens tabs on daily basis with dozen extensions, and even worse if these extensions use some JS frameworks just to use some simple feature...