Expose prefs for tabs-on-demand

Feature	Status	Dev Lead	QA Lead	Status
Expose prefs for tabs-on-demand	Landed in Firefox 8	Paul O'Shannessy	Mihaela Velimiroviciu

Summary

Firefox 4 has the hidden ability to load tabs on-demand by setting the maximum number of concurrent tabs being restored to "0" — now that the feature has been in the wild for a while, we'd like to expose it as the default behavior for session restore. It makes startup a lot faster, and uses a lot less memory.
This feature falls primarily in the Experience category (from the "Discover, Experience, and Connect" vision statement.)
This feature is available starting Firefox 8.