2059571 - Tracker count in URL bar animates open on every tab switch, even when switching between two tabs showing the same site

Status: NEW

(Firefox :: Protections UI, enhancement, P3)

Description

[Daniel Holbert [:dholbert]]

STR:

1. In a fresh Firefox profile, open two tabs, both viewing a site that has some tracker that triggers our tracker-count UI.
   e.g. https://www.moody.edu/ gives me a tracker-count between 1 and 3 (with default ETP settings and no adblocker installed).
   Or you can use e.g. https://www.yahoo.com/ which gives me a tracker count of >100 (not always the same exact number; depends on exact ad load etc.)
2. If the long-form tracker count displays (N trackers blocked): either wait ~20 seconds or shrink your window horizontally, so that it collapses down to just a number.
3. Switch back and forth between the tabs with Ctrl+Tab.

ACTUAL RESULTS:
The tracker-count animates or flickers out-of and back-into existence on every tab-switch (even though I'm switching back and forth between two tabs that were both already showing it)

EXPECTED RESULTS:
The tracker count shouldn't disappear-and-then-reappear when I'm switching between these tabs. Probably it should just get swapped atomically with the rest of the URL bar contents (which in this case means you wouldn't see any change as you switch tabs, other than maybe the number if one tab had 2 trackers blocked and the other had 3)

I'm using Firefox Nightly 155.0a1 (2026-07-29) (64-bit) on Ubuntu 26.04

Comment 1

[Daniel Holbert [:dholbert]]

Attachment: screencast of bug (tracker count flickers very briefly)

Comment 2

[Daniel Holbert [:dholbert]]

My screencasting tool doesn't record with a high enough frame-rate to capture all of the flickering that I actually see on my screen, but it does show some of it; e.g. just after t=2s, ther's a moment where the number 1 disappears and only a shield shows, before the 1 quickly reappears.

Comment 3

[Daniel Holbert [:dholbert]]

The user-facing issue here isn't so much about the tracker count itself, but rather that the rest of the URL bar gets jiggled around due to this rapid flicker.

Comment 4

[Daniel Holbert [:dholbert]]

Attachment: screencast of bug (tracker count animates smoothly into existence)

Sometime the tracker count flickers as shown in my previous screencast; other times it animates smoothly into existence as shown here.

The smooth-animation looks less glitchy perhaps, but it still feels unnecessary/unexpected.

Comment 5

[BugBot [:suhaib / :marco]]

The severity field is not set for this bug.
:emz, could you have a look please?

For more information, please visit BugBot documentation.

Comment 6

[BugBot [:suhaib / :marco]]

The severity field is not set for this bug.
:emz, could you have a look please?

For more information, please visit BugBot documentation.

Comment 7

[Emma Zühlcke [:emz]]

Vincent, could you please take a look? Feel free to set priority / severity too.