+++ This bug was initially created as a clone of Bug #1696793 +++

I can still reproduce a similar issue to Bug 1696793 with the fix applied. The STR are a little bit different and doesn't always happen:

STR:

1. Ensure prompts.windowPromptSubDialog = true.
2. Close the browser window with quit warning enabled and at least two open tabs.
3. Modal dialog appears, press ESC to close it and quickly click the window close button again.
4. Quickly repeat step 2 and 3 until the close window button stops to function.

Expected:

Browser continues to operate normally after modal dialog dismissed.

Actual:

Modal dialog goes away but many things stop working, the new tab button is greyed out as well as many menu items. Cannot close window or quit, only apparent way to recover is to terminate the application or close all remaining tabs.
Using these STR I also get a shutdown hang, see Bug 1696397. There are already patches to address this issue, so only the UI disabled issue remains.

Tested on Linux on today's Nightly.

Here is a video showing the issue. Note that this is with the shutdown hang fixes applied. So when closing all tabs the browser shuts down properly.

I can reproduce it 100% by pressing and holding ESC while clicking the close button.

Paul is looking into this more - thanks!

Set release status flags based on info from the regressing bug 1685313

It looks like this is MR1 only, so setting disabled for tracking 87 - let me know if that's wrong.

Marking as P1. Per experience review we agreed to mark as P1 bug the ones that will block MR1.

https://hg.mozilla.org/mozilla-central/rev/07524a7905f9