1997790 - Tab hover preview appears for wrong tab when state changes during loading

Status: VERIFIED FIXED

(Firefox :: Tabbed Browser, defect, P2)

Description

[Kestrel]

Attachment: Hover previews appearing for wrong tabs as they load

STR:

1. Visit a website that loads slowly like https://inv.nadeko.net on latest Nightly 146.0a1.
2. Open several video links in background tabs.
3. While the tabs are still loading, quickly pass the mouse cursor over them before they finish loading.
4. Keep cursor hovered over last tab until tabs finish loading.

Expected:
Tab hover preview for last tab is shown the whole time.

Actual:
Tab hover preview appears for each tab as state changes during loading despite cursor not hovering over them.

Regression window:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=a4bf251f5ffc5a502a2d4fd6794714cac3ffa2c1&tochange=27a57130e67c0d4ecb79abd6e194199f0a79b656

Regressed by Bug 1991082.

Comment 1

[BugBot [:suhaib / :marco]]

:jswinarton, since you are the author of the regressor, bug 1991082, could you take a look? Also, could you set the severity field?

For more information, please visit BugBot documentation.

Comment 2

[Jeremy Swinarton]

I am also able to reproduce this by opening a Youtube video, paging to a few seconds before the end, and while the video is finishing, hover over the youtube tab, and then hover onto a different tab and stay there. After the video ends, Youtube auto starts another video and changes the tab title, which causes the panel to shift back to the Youtube tab.

The underlying cause is this call: https://searchfox.org/firefox-main/source/browser/components/tabbrowser/content/tab-hover-preview.mjs#258 which sets up a listener on TabAttrModified. It is removed in the corresponding deactivate call. But, if the tab panel moves (and is not deactivated), the listener is not deregistered, and we have a situation where multiple tabs have the listener (only the active tab should have it).

Comment 3

[BugBot [:suhaib / :marco]]

Set release status flags based on info from the regressing bug 1991082

Comment 4

[Jeremy Swinarton]

This should be fixed by the most recent patch landed on bug1980036: https://phabricator.services.mozilla.com/D271783

Rares, would you or someone else mind verifying this fix works as expected? Thank you!

Comment 5

[Kestrel]

Confirmed fixed on latest Nightly 147.0a1 (2025-11-13).

Fix window:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=1f95ad791ce4b08ed07c43766b26a967b56d15f4&tochange=2b924dd17fc7d417a1098a70dbf088bf14bae3fc

Fixed by Bug 1980036.

Comment 6

[Rares Doghi, Desktop QA]

I was able to reproduce this issue and verify the fix in our latest Nightly 147.0a1 (2025-11-13)

Comment 7

[Rares Doghi, Desktop QA]

Updating the main status flag.