I get the same issue at https://www.flexboxpatterns.com/mosaic:
Ah, so if the flexbox is scrolled inside a div we don’t detect any mopvement when it is scrolled… I’ll create a simpler test case.
Bug logged: https://bugzilla.mozilla.org/show_bug.cgi?id=1511426
Thanks for letting us know about this issue!
Great. Thanks! Guess I could have mentioned that the flex container was scrolling 
it is very good idear!
i am looking some ruler …
like thiese…
Thank you… very very much~:grin: