1972003 - Reenable browser_multiselect_tabs_reorder.js on Windows

Status: NEW

(Firefox :: Tabbed Browser, task, P2)

Description

[Nikki Sharpley (:nikkis) (she/her)]

For context, this is the patch that needed to land that's causing a mysterious failure and skips the test for Windows: https://phabricator.services.mozilla.com/D247132
This is the failing test: https://treeherder.mozilla.org/jobs?repo=try&revision=4894ead959a4b46eafdb2fb39f6e2ff59339bace (profile with screenshots attached)
Its failing at this block: https://searchfox.org/mozilla-central/rev/240ca3fb4457621e155d039c7ea7055c0e22b374/browser/components/tabbrowser/test/browser/tabs/head.js#321-323
But here's the catch, the failing test, browser/components/tabbrowser/test/browser/tabs/browser_multiselect_tabs_reorder.js, is not reproducible locally on ANY platform. It only fails on Windows on try.
The test is selecting tabs [1 ,3 ,5], then using tab 3 to drag to position 4. In the screenshot, it appears tab 3 is still in position 3 (we don't want that) and the logs I've added in previous tries confirm this. Testing this manually in Windows and running the tests locally on Windows, this all works. So its a mystery why on try it does not.

Its disabled for now with QA testing the original patch to confirm no bugs, and this as a follow up bug to fix/enable this test for Window.

Comment 1

[Stephen Thompson [:sthompson]]

On Windows debug 141.0a1 (2025-06-13) (64-bit).

On current main https://github.com/mozilla-firefox/firefox/commit/baa374a651997687e62a7cb71f950133c0c0a238 I do not experience test failures for browser_multiselect_tabs_reorder, even with many iterations using --verify.

After applying https://phabricator.services.mozilla.com/D247132 in the patch stack, I still do not experience test failures.

After applying https://phabricator.services.mozilla.com/D252525 in the patch stack, I still do not experience test failures.

But after applying https://phabricator.services.mozilla.com/D253235 in the patch stack, I do get a failure.

I'll try to dig into the effects of https://phabricator.services.mozilla.com/D253235 on browser_multiselect_tabs_reorder