The autoconfirmed group is configured so that it requires the user to have made at least some number of edits and to be of at least some age (typically 10 edits and 4 days).
This mechanism can be abused by some LTAs, who create "sleeper" accounts, which become active only after the time required for autopromotion – so that they can become autoconfirmed after a few minutes of editing. This is risky and reduces the opportunities for community to look at the edits before user can excercise benefits of being autoconfirmed.
Therefore, we should change the configuration for being autoconfirmed, so that it uses APCOND_AGE_FROM_EDIT, instead of APCOND_AGE. The value of $wgAutoConfirmAge won't change.
This will be done only on wikis where $wgAutoConfirmCount > 0.