448662 - position:absolute with bottom specified references to viewport like position:fixed

Status: RESOLVED DUPLICATE of bug 105286

(Firefox :: General, defect)

Description

[Andrei Boros]

User-Agent:       Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.8.1.16) Gecko/20080702 Firefox/2.0.0.16
Build Identifier: Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.8.1.16) Gecko/20080702 Firefox/2.0.0.16

Have an element positioned with CSS: 
position: absolute;
bottom: 0px;

Assume the page has vertical scrollbar. The positioned element behaves somewhat like position:fixed, in the following aspect : 
- it is positioned at the bottom of the viewport (so the reference is the viewport)
- as opposed to position:fixed, it does scroll. 

AFAIK, from CSS2 specs : 

==============================================================
absolute
The box's position (and possibly size) is specified with the 'left', 'right', 'top', and 'bottom' properties. These properties specify offsets with respect to the box's containing block. 

fixed
The box's position is calculated according to the 'absolute' model, but in addition, the box is fixed with respect to some reference. In the case of continuous media, the box is fixed with respect to the viewport (and doesn't move when scrolled).

...

Containing block : 
The root of the document tree generates a box that serves as the initial containing block for subsequent layout.
====================================================

For position absolute, the containing block should be the root of the document, also for bottom. Why the reference to the viewport? The initial containing block gets sized according to the content, absolutely positioned or not, hence you get scrollbars. If you get scrollbars, then the bottom property should reference the initial containing block, not the viewport, the reference being the bottom of the document. 

Reproducible: Always

Steps to Reproduce:
1.
2.
3.

Comment 1

[Gérard Talbot]

This is a DUPLICATE of bug 105286.
[
How should we treat "position:absolute; bottom: 0"?  Should it be at
the very bottom of the page or at the bottom of the viewport when the page first
loads?
]
was answered, decided in bug 105286

Therefore, resolving as a DUPLICATE of bug 105286

Comment 2

[Gérard Talbot]

It was also a duplicate of bug 196937