This issue does not happen in R68-10687 test image.

Flags in /etc/chrome_dev.conf:

--kiosk
--login-user=chronos
!--login-manager

Albert, are you able to help route this to folks familiar with Kiosk on Chrome OS?

Chenghan, please bisect ChromeOS versions to determine when this started failing.

Kiosk mode was working in 10718.4.0 but failed in 10718.6.0

Those two versions are both on the R68 release branch, and 


These two versions do have different Chromes:

10718.4.0 - 68.0.3440.4
10718.6.0 - 68.0.3440.7

And, luckily, since these two versions are on the R68 release branch, the Chrome diffs are all cherry-picks (and a small list of them too):

https://chromium.googlesource.com/chromium/src/+log/68.0.3440.4..68.0.3440.7?n=10000

1b1f9e5 [Fullscreen Control] Roll the fullscreen exit UI to 100% on all channels by Yuwei Huang
4a049d4 Make FrameSelection::Contains return false for null VisibleSelection in DOM tree by Xiaocheng Hu
c6ac28e (Re)allow copying image documents directly by Xiaocheng Hu
1c94827 [Merge to M-68] Enable Initial Enrollment for official builds and detect outdated server by Pavol Marko
eea6b3c m68: Revert "Reland "Enable ChromeVox ARC support for all apps"" by David Tseng
744657f Picture-in-Picture: set proper DisplayType and some cleanups. by Mounir Lamouri


That first patch sounds very suspicious:
"Roll the fullscreen exit UI to 100% on all channels"

This landed originally in:
https://chromium-review.googlesource.com/c/chromium/src/+/1073625

It was implemented for issue 829606 "Fullscreen exit FAB" which "adds a UI element (Floating Action Button) to facilitate exiting fullscreen mode in Chrome desktop in cases where a keyboard is not present or overridden".

This Cl landed on master @ 69.0.3441.0.


Chrome 69.0.3441.0 was first included in Chrome OS R69-10726.0.0 (2018-05-27 03:14), which is probably what you'd find if you bisect ToT instead of the R68 branch.

yuweih,
Is there a way to disable the "Exit fullscreen" "Floating Action Button" in kiosk mode?

I think this is fixed in 68.0.3440.84. See  bug 867309 

Before the fix is rolled out, you can turn off the fullscreen exit UI flag:
chrome://flags/#enable-experimental-fullscreen-exit-ui

Thanks yuwieh....  in which ToT Chromium version did the fix land?

I think that is 70.0.3503.0..

Correct.  [0] is in 70.0.3505.0 [1] which is part of Chrome OS R70-10919.0.0+
[0] f4f6871 Disable fullscreen exit UI when kiosk mode is on
[1] https://chromium.googlesource.com/chromium/src/+log/70.0.3502.0..70.0.3505.0?n=10000