User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:126.96.36.199) Gecko/2009042316 Firefox/3.0.10 (.NET CLR 3.5.30729)
Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:188.8.131.52) Gecko/2009042316 Firefox/3.0.10 (.NET CLR 3.5.30729)
First, the element being resized should be within an element with overflow-x:auto or overflow-y:scroll.
For a page with a 120px header, 40px div on top and 80px div below, if the elements are updated with JS such that the 40px element grows to 120px and the 80px element shifts to display:none, then there's a moment where both new 120px and old 80px elements display.
The expectation would be that while the JS block is being processed the div elements wouldn't dynamically jump around.
Steps to Reproduce:
1. See attached file
2. Click the button a few times
Red element flickers as the blue element grows.
A clean transition for both elements. This happens if no overflow-x:auto or overflow-y:scroll is set.
Created attachment 380393 [details]
Page that demonstrates display: switch flicker.
This may be related to 477789, but this doesn't cause a full screen flicker.
This regressed in 2004, in at least two steps. After the flickering started, this changed again at least two times.
I have tested your issue on latest FF release (46.0.1) and latest Nightly build and could not reproduce it. I have opened the testcase you provided in comment 0 and clicked multiple times the button, but there was no flicker.
Is this still reproducible on your end ? If yes, can you please retest this using latest FF release and latest Nightly build (https://nightly.mozilla.org/) and report back the results ? When doing this, please use a new clean Firefox profile, maybe even safe mode, to eliminate custom settings as a possible cause (https://goo.gl/PNe90E).