In bug 1172167 we noticed that killed apps, because of OOM are not showing up in the task manager (cards view). This is a bug and was something that was supposedly fixed in bug 941238 (at least if I understand bug 941238, comment 18 correctly). From bug 1172167, comment 12: " I'm a bit confused still though, if the apps are getting killed by the LMK (or by gecko in general), they should be in a suspended state and still on the stack (as managed by StackManager, where TaskManager gets its app list from.) That was the point of bug 941238. If we don't feature these apps in the task manager, it is a fairly pointless feature for low-memory devices as OOM with multiple apps running is the normal and expected state (memory regressions notwithstanding) So, apps getting killed more frequently by the LMK due to low-memory may well be regression, but they should continue to be represented as cards in the task manager; selecting such a card revives that app. "

As far as I can tell, this was fallout from bug 1094759. We used to have a AppWindow.SUSPENDING_ENABLED which tracked the value of the app-suspending.enabled settings. Since bug 1094759, AppWindow asks if Service.query('suspendingAppWindow'), but this state is never registered. The unit tests pass because we mock the Service to assert on how AppWindow responds when the value is true/false. There is an observer for the value of this setting in AppWindowManager, but all it does is kill existing suspended AppWindows, it doesn't register or toggle the suspendingAppWindow state.

Marking WONFTIX, sorry for the bug spam. If somebody still wants to work on this, please open a new bug.