Created attachment 296665 [details] test case Steps to reproduce the problem: Load the test case or go to https://www.w3.org/Style/CSS/Planet/ What is the expected behavior? Document scrolls vertically What went wrong? Document scrolls horizontally Did this work before? Yes Does this work in other browsers? Yes
Created attachment 296666 [details] proves the issue does not repro in normal mode
Found likely duplicate
It is indeed a dupe. *** This bug has been marked as a duplicate of bug 164891 ***