1718841 - Elements with position: fixed don't grow to reserve space for a vertical scrollbar when the need for a vertical scrollbar changes

Status: RESOLVED DUPLICATE of bug 764076

(Core :: Layout: Scrolling and Overflow, defect)

Description

[mark.falconbridge]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:89.0) Gecko/20100101 Firefox/89.0

Steps to reproduce:

Using the jsfiddle here - https://jsfiddle.net/xp8e396s/1/ in a Windows 10 environment
(1) Go to the jsfiddle above and click the "Toggle Content Height" button
(2) Notice that a vertical scroll bar is added (this is correct) but no extra space is used for it so the content is hidden.
(3) Note that a horizontal scroll bar is also added, this is incorrect as the content hasn't yet reached the max-width.

Actual results:

No extra space was provided for the vertical scroll bar so the content is obscured.
A horizontal scroll bar was added.

Expected results:

Extra space should be reserved for the vertical scroll bar so that the content can be fully seen up until a max-width is hit.
The horizontal scroll bar should only be added when the max width has been reached.

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The Bugbug bot thinks this bug should belong to the 'Core::Panning and Zooming' component, and is moving the bug to that component. Please revert this change in case you think the bot is wrong.

Comment 2

[Daniel Holbert [:dholbert]]

This is a version of bug 764076. The problem here is that we're not making the fixed-position element wide enough to account for the scrollbar (which we hypothetically could do, but it's complicated).