1164724 - Surface warn before quitting pref for Mac users

Status: RESOLVED DUPLICATE of bug 645338

(Firefox :: Settings UI, defect)

Description

[Stuart Philp :sphilp]

Attachment: Screen Shot 2015-05-13 at 7.47.23 PM.png

This request is for similar functionality to Chrome's "Warn Before Quitting" app menu item, see screenshot, 3rd item from the bottom.

On OSX, hitting CMD-Q force quits Firefox without a prompt. There is a pref to turn on a prompt, browser.showQuitWarning, but I don't see it exposed anywhere in the settings or the app menu (where most regular users would look for it). We should surface this pref so more Mac users will see it.

There's some related discussion in bug 565567 about having the prompt vs the existing session state stuff, but this new bug is purely about surfacing the prompt pref in the app menu (or in the main settings somewhere). 

Reasoning: Some users will prefer to have Firefox not remember session state, but also not allow for accidental force quits.