[Bug] tab-counter vanishing on active tab

[jeff-etched]

Abstract

The tab-counter element in a tab-item disappears when the tab becomes the active one.

Steps to reproduce

1. Start Firefox with clean profile.
2. Install TST. (Appearance left as default "Proton")
3. Create and collapse a tab tree and at least one other tab not in that tree.
4. Switch between the collapsed tree root and the other tab
5. Select No Decoration and repeat step 4.
6. Specify an active tab background color in User Style Sheets and repeat step 4

Specifying only a background-color for tab-item.active .background (as per the snippet example):

tab-item.active .background { background-color: steelblue; }

Expected result

The tab-counter on a collapsed tree remains when the tree is selected, both in the default config and with a style sheet background color specified. For configurations with hidden tab-twisties, there is currently no visual distinction between an active tab that is a leaf node or a collapsed parent.

Actual result

The tab-counter of the collapsed root tab disappears when the tree is selected and the close button appears. Notably, if the 'crop with ".."' option is selected, it is apparent that the tab-counter is being pushed to the left and not rendered, not simply rendered over, due to whitespace appearing between the ellipses and the X.

Only with No Decoration and no User Style Sheet specified does the text element remain visible.

is selected, the tab-counter of the collapses tree becomes visible.

Environment

• Platform (OS): x86_64 Tuxedo Linux 24.04.3 LTS (Ubuntu derivative with KDE Plasma 6.5.2 Wayland)
• Version of Firefox: 146.0
• Version (or revision) of Tree Style Tab: 4.2.7

[jeff-etched]

For both the clean install default and for No Decoration plus specified active tab background color, the collapsed child count is missing:

When No Decoration is used and no User Style Sheet active tab background color is given, it appears (active tab text color specified just for visual indication here):

[irvinm]

@piroor / @jeff-etched, I was able to see this behavior and wanted to check the CSS when it occurred. It looks like the tab counter element is there, but just being obscured by the fade away of the label text. I'm sure this can be easily fixed by @piroor.

However, one thing I noticed in a clean install with just TST and uBlock Origin installed was some strange vertical scrolling and hiding of tabs that can clearly fit in the sidebar. It seems to be related when you have a "new tab" as the active tab. You can see from these clips when a new tab is selected that the top tab sometimes gets clipped and is not even scrollable to it. If you pin a tab, then it is the pinned tab row that is hidden.

Example of hidden counter when selected ... and exploration of how to demo the hidden tabs.

2026-01-08_09-12-45.mp4

Active example of "new tab" behavior which is easily reproducible (No clicking, just mouse movement)

2026-01-08_09-16-51.mp4

[piroor]

This looks to be caused by a missing z-index of the span.ui element which is a grand parent of both the tab label and the counter. The commit 30ff224 fixes it so this does not happen with the latest development build of TST. (So this is an accidental fix.)

A new release including the commit is not released yet due to dogfooding for high impact changes. Now it looks to be the time to release - I enoughly dogfooded those changes.

[github-actions]

This issue has been closed due to no response within 14 days after labeled as "fixed", 7 days after last reopened, and 7 days after last commented.