“browser.showQuitWarning” config was removed from Firefox 63. It was a convenient and perfectly working feature that I really have no idea why it had to be removed. It was brought up in bugzilla with many comments but since it was not a bug I was afraid it would just get forgotten so I wanted to bring it up agian.
One of the things I like about Firefox is the ability to customize small settings. This quitWarning dialogue was one of them. There is a new item in the options menu that is less useful, and only let us save all the time or dont save at all. This is more like the browser making decisions for us and not the other way around. What’s the point of Firefox if you just make it more like Chrome?
For now I switched to Firefox ESR but it wont last for long. Why did you removed this in the first place? and please bring back more control to us.