1955340 - Vertical tabs with expand on hover show a transparent background when using Mica on Windows

Status: VERIFIED FIXED

(Firefox :: Sidebar, defect, P2)

Description

[Mathis Paquet]

Attachment: Screenshot 2025-03-20 113741.png

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:138.0) Gecko/20100101 Firefox/138.0

Steps to reproduce:

1. Set widget.windows.mica to true on Firefox Nightly on Windows
2. Enable vertical tabs
3. Enable expand on hover
4. Hover the vertical tabs

Actual results:

The background is completely transparent.

Expected results:

The background should use the same Mica effect as the vertical tabs.

Comment 1

[BugBot [:suhaib / :marco]]

The Bugbug bot thinks this bug should belong to the 'Core::Widget: Win32' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Comment 3

[Olli Pettay [:smaug][[e-mail]]]

there is --toolbox-bgcolor: ActiveCaption; which seems to trigger the transparency.
https://searchfox.org/mozilla-central/rev/e44c234b5635d42d9cefd89c604b73be0aa4bd79/browser/themes/shared/browser-colors.css#11-12

Comment 5

[Takanori MATSUURA]

This problem occurs with the Automatic theme.
Using the Light or Dark theme works fine.

Comment 6

[Mathis Paquet]

(In reply to Takanori MATSUURA from comment #5)

This problem occurs with the Automatic theme.
Using the Light or Dark theme works fine.

Mica doesn't work with dark or light theme, only with auto.

Comment 7

[Sarah Clements [:sclements]]

Emilio is there a timeline for rolling out widget.windows.mica to all users?

Comment 8

[Emilio Cobos Álvarez [:emilio]]

As with the macOS translucency, it needs UX to make the call.

Comment 9

[Emilio Cobos Álvarez [:emilio]]

Attachment: Bug 1955340 - Ensure sidebar-main is opaque when expanded-on-hover with Windows Mica. r=kcochrane!

This makes it behave effectively the same as with the macOS system
theme.

Comment 10

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/8883700f770d
https://hg.mozilla.org/integration/autoland/rev/1853826c8c34
Ensure sidebar-main is opaque when expanded-on-hover with Windows Mica. r=kcochrane,sidebar-reviewers

Comment 11

[Atila Butkovits]

https://hg.mozilla.org/mozilla-central/rev/1853826c8c34

Comment 12

[Dianna Smith [:diannaS]]

:emilio is this something you want to call out in the fx142 release notes? Please nominate if so.

Comment 13

[Emilio Cobos Álvarez [:emilio]]

Probably not, mica is disabled by default.

Comment 14

[Bianca Hidecuti, Desktop Test Engineering [:bhidecuti]]

I was able to reproduce the issue with an affected Firefox Nightly 138.0a1 build from 2025-03-20 on Windows 11, as described in Comment 0.
Verified as fixed using Firefox 142.0b4 on Windows 11. Vertical tabs with expand on hover are now opaque.