1984922 - Unloaded tabs lose the gray favicon when dragged to a new window

Status: VERIFIED FIXED

(Firefox :: Tabbed Browser, defect, P3)

Description

[pokechu022]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:142.0) Gecko/20100101 Firefox/142.0

Steps to reproduce:

1. Open 2 tabs of https://en.wikipedia.org/wiki/Main_Page
2. Open a new window
3. In the original window, switch to the first tab.
4. Right-click on the second tab and select "unload tab". The favicon should turn grey (or black for Wikipedia, I guess)
5. Hold shift and select the second tab, creating a selection containing the first and second tabs.
6. Drag the first tab into the new window. The second tab should move with it. (Dragging the second tab would load it immediately, which would not reproduce the issue.)

Actual results:

The icon reverts back to its original appearance, but the tab remains unloaded (based on the lack of a preview when hovering over it, and the lack of a PID in nightly).

Expected results:

The icon should have remained grayed out, since the tab was manually unloaded.

Also reproduced on Nightly 144.0a1 (2025-08-22).

Comment 1

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

The Bugbug bot thinks this bug should belong to the 'Firefox::Tabbed Browser' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Comment 2

[Ardelean Oana, Desktop Test Engineering [:oardelean]]

Hello, thank you for the bug report!
Managed to reproduce this issue on:

• Firefox Nightly 144.0a1;
• Firefox 143.0b4;
• Firefox 142.0;

Tested on:

• Windows 10;
• Ubuntu 22;
• macOS 15;

Setting as NEW so the developing team can have a look.

Comment 3

[Stephen Thompson [:sthompson]]

Manually unloaded tab gets both pending and discarded attributes. It looks like the tab loses the discarded attribute but keeps the pending attribute when it goes to another window.

This might just require persisting discarded within Tabbrowser.swapBrowsersAndCloseOther. Tabbrowser.swapBrowsersAndCloseOther has a separate Session Restore code path for pending tabs that might also require additional handling of the discarded state but I'm not sure.

Comment 4

[Greg Stoll :gstoll]

Attachment: Bug 1984922 - propagate "discarded" attribute when an unloaded tab moves windows r=#tabbrowser-reviewers!

Also add tests that verify this behavior.

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/179007e0656c
https://hg.mozilla.org/integration/autoland/rev/6e091c804eec
propagate "discarded" attribute when an unloaded tab moves windows r=tabbrowser-reviewers,sthompson

Comment 6

[agoloman]

https://hg.mozilla.org/mozilla-central/rev/6e091c804eec

Comment 7

[Ardelean Oana, Desktop Test Engineering [:oardelean]]

Issue is reproducible on a 2025-09-04 Firefox Nightly build on Windows 10.
Verified as fixed on Firefox Nightly 145.0a1 and Firefox 144.0b2 on Windows 10, Ubuntu 22, macOS 15.