See: https://wiki.mozilla.org/User:Mconnor/PrivateBrowsing

It seems this requires a lot of support from Mozilla itself, and we'll have to wait for such support to
exist.  Even the stuff discussed on the linked page does not sound very proper.  It seems to just be a
hacked-together way of getting things working as easily as possible given the limitations of how existing
things work in Mozilla.

There are measures we can take now, such as disabling disk caches,
cookies, and history when privacy-mode is enabled.

Improper and hacked-together or not, as conkeror is based on mozilla,
unless we fork xulrunner, its what we have (or will have) to work
with.

Please don't call it porn-mode.  Please.

https://developer.mozilla.org/en/Supporting_private_browsing_mode

https://wiki.mozilla.org/PrivateBrowsing

nsIPrivateBrowsingService is currently a Firefox-only service.  It doesn't seem to be something that has
specific dependencies on Firefox though, that would not apply to other mozilla programs, so I think there
is a fair chance that xulrunner will have this feature before long.