There is no concrete plan for enabling support for any particular draft SPDY spec in any particular version of Firefox yet. There's no way it will be enabled by default in Firefox 11. Our implementation needs a lot more testing, especially since there are already very important SPDY-enabled sites live on the Internet. Even if we spit out a perfect implementation of the latest draft spec on the first attempt, it might be the case that these existing sites depend on behavior undefined by the spec and/or bugs in Chrome. These kinds of issues still need to be found and addressed.
There is also still work that needs to be done on the spec itself. I suspect there will be many rounds of divergence and convergence in SPDY implementations as more people experiment with implementing it, and as the protocol improves.
Certainly Google's sites qualify as important, but are any other major sites using it? Chrome doesn't seem to setup SPDY sessions for anything I visit regularly other than Google sites.
BTW, I heard an unsubstantiated rumor Netflix has added SPDY, although this might be due to the Chromebook plugin.