From menu select edit/preferences and double-click on the advanced tab. There used to be a checkbox at the end saying "warn me before accepting cookies." This has suddenly vanished. On a lesser note, the second radio button under cookies ("accept only cookies that get sent back to the original server") has its text appearing below the button instead of alongside it. Note worth opening up a separate bug report on something so minor so I'm just including it as an addenda to this bug report. Using a tree that was pulled and built a few hours ago.

Can we get this bug fixed for M10?

*** Bug 12857 has been marked as a duplicate of this bug. ***

This is fixed now.

Yes, it's fixed, 19990928xx builds.

Bulk move of all Pref UI component bugs to new Preferences component. Pref UI component will be deleted.