Re: Et mozilla ?

Pas du tout, la position de ton element est specifiee par rapport au premier element parent dont la propriété "display" est definie.
De même, le fait que la propriete display l'element parent soit de type block ou inline importe peu

http://www.w3.org/TR/CSS21/visudet.html#containing-block-details(...)

4. If the element has 'position: absolute', the containing block is established by the nearest ancestor with a 'position' of 'absolute', 'relative' or 'fixed', in the following way:

1. In the case that the ancestor is inline-level, the containing block depends on the 'direction' property of the ancestor:
1. If the 'direction' is 'ltr', the top and left of the containing block are the top and left content edges of the first box generated by the ancestor, and the bottom and right are the bottom and right content edges of the last box of the ancestor.
2. If the 'direction' is 'rtl', the top and right are the top and right edges of the first box generated by the ancestor, and the bottom and left are the bottom and left content edges of the last box of the ancestor.
2. Otherwise, the containing block is formed by the padding edge of the ancestor.

If there is no such ancestor, the containing block is the initial containing block.