2012395 - Animation of collapsing/expanding group with selected tab is not smooth

Status: UNCONFIRMED

(Firefox :: Tabbed Browser: Tab Groups, defect)

Description

[Merci chao]

Attachment: 2026_01_26_15_26_27.mp4

Steps to reproduce:

1. Open several tabs and a group with multiple tabs, don't make the tab strip overflow;
2. Select a tab in the group, collapse/expand the group;
3. Tabs will flicker slightly during the animation, due to the displaying/hiding of the overflow counter.

Lengthening the width transition can make the issue more observable:

#tabbrowser-tabs {
  --tab-width-transition: min-width 1000ms ease, max-width 1000ms ease !important;
}

Comment 1

[Merci chao]

Attachment: 2026_01_26_15_38_23.mp4

Here is another version with normal speed, where one of the tabs is highlighted.

• When collapsing the group, tabs outside first shrink due to the presence of the overflow counter, then begin expanding once the group collapses.
• When expanding the group, tabs first expand due to the hiding of the counter, then begin shrinking as the group expands.