1364436 - Close button does not stick at the bottom of the menu page in three.js demo

Status: NEW

(Core :: General, defect)

Description

[Bogdan Maris, Desktop QA]

[Affected versions]:
- Windows 7 64bit
- Windows 10 32bit
- Ubuntu 16.04 64bit
- Mac OS X 10.11.5

[Affected platforms]:
- Firefox 53.0.2
- Firefox 54.0b7
- latest Nightly 55.0a1

[Steps to reproduce]:
1. Open https://threejs.org/examples/#webgl_animation_skinning_morph
2. Open all the dropdowns from upper right (Clip 'Action', Clip 'facialExpressions' etc)
3. Scroll through the menu from right

[Expected result]:
- Close Controls button stays at the bottom of the page.

[Actual result]:
- Close Controls moves up the menu when scrolled.

[Regression range]:
- This is not a recent regression. I used mozregression and found a range:
16:05.75 INFO: Last good revision: 37516445a0b5 (2014-01-10)
16:05.76 INFO: First bad revision: e89afc241513 (2014-01-11)
16:05.76 INFO: Pushlog:
http://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=37516445a0b5&tochange=e89afc241513
- Note that I considered GOOD build one that did not display anything.

[Additional notes]:
- I attached a screencast for this issue.
- I am not sure if this is the right component for this, please change it if necessary.

Comment 1

[Mats Palmgren (inactive)]

At first glance, this appears to be the correct rendering for the given markup
and styles.  The "Close Controls" element is abs.pos. with 'auto' top/left
so it will be placed after the previous element, which is an <ul style="height:780px">
or some such.  It appears that the 'height' there is set by JS; you can see this
by opening devtools Inspector and then dragging the splitter between the devtools
and content so that its height is resized - the attribute is updated when you do
this.  So, it seems the JS calculating this height value is wrong in some way.

I don't see any relevant Layout/CSS/DOM changes in the indicated pushlog though.
A smaller testcase would be nice...