1476925 - Negative margin doesn't cancel the padding on parent causing undesired line breaking when width is auto

Status: RESOLVED DUPLICATE of bug 1502610

(Core :: Layout: Block and Inline, defect, P3)

Description

[roxleitan]

Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:63.0) Gecko/20100101 Firefox/63.0
Build ID: 20180718220144

[Affected versions]:
Nightly 63.0a1, Firefox Beta 62.0b9

[Affected platforms]:
Windows 10 x64, Mac OS X 10.13

[Steps to reproduce]:
1.Launch Firefox with a new profile
2.Go to https://edition.cnn.com/entertainment
3.Hover using mouse over "watch this" or "top stories"

[Expected result]:
The selection should be correctly highlighted 

[Actual result]
The selection is overlapped while is highlighted

Comment 1

[Jonathan Kew [:jfkthame]]

This appears to be a layout issue; the overlapping occurs because those headings unexpectedly wrap onto two lines, whereas in other browsers they appear on a single line.

Comment 2

[Jonathan Kew [:jfkthame]]

Attachment: reduced testcase - compare behavior in Firefox vs Chrome/Safari/Edge

In Firefox, the text here is broken across two lines, whereas in all the other browsers I've tested (Safari, Chrome, Edge) it remains on a single line.

Comment 3

[roxleitan]

The issue is reproducible also on Firefox Release 61.0.1

Comment 4

[Scott]

I just came across this problem too, and made a JSFiddle: https://jsfiddle.net/brLfc14a/
This example uses Flexbox but the same happens if you remove flex and float the list items.

It seems that whenever you add negative margins the width of the element decreases, but it has always been my understanding that negative left/right margins increase the width of the element.

I'm using Firefox 65.0 (macOS 10.14.2).

Comment 5

[Mats Palmgren (inactive)]

Looking at jfkthame's testcase, it appears to be essentially the same issue as in bug 1502610.

Comment 6

[Firefox Bug Husbandry Bot]

Migrating Webcompat whiteboard priorities to project flags. See bug 1547409.

Comment 7

[Firefox Bug Husbandry Bot]

See bug 1547409. Migrating whiteboard priority tags to program flags.

Comment 8

[Daniel Holbert [:dholbert]]

(In reply to Mats Palmgren (:mats) from comment #5)

Looking at jfkthame's testcase, it appears to be essentially the same issue as in bug 1502610.

That bug and this bug are in fact both dupes of much-older bug 871224. Marking as such.

Comment 9

[Daniel Holbert [:dholbert]]

Sorry, my mistake -- per bug 871224 comment 27, it turns out Chrome has changed behavior and matches us on that bug's testcases now. But they still disagree with us on the testcase here, and the padding-right is now the key thing that causes testcases to have differing behavior. So this is not a dupe of bug 871224.

So let's use bug 1502610 as the dupe-target for this family of bugs. Technically this one here was filed first, but bug 1502610 has simpler testcases and more spec discussion, so it's a better place to focus the conversation.