1874903 - ClearType is partially disabled when any sidebar panel provided by addons is shown

Status: NEW

(Core :: Graphics: WebRender, defect)

Description

[YUKI "Piro" Hiroshi]

Attachment: Testcase xpi

Steps to reproduce

1. Prepare a Windows environment with activated ClearType.
2. Start Firefox with clean profile.
3. Set the bookmarks toolbar always visible. (right-click on the toolbar and choose "Bookmarks Toolbar" => "Always Show")
4. Go to about:debugging.
5. Load the attached testcase addon as a temporary addon.
6. Confirm that the sidebar panel is switched to the one provided by the testcase addon.

Expected result

All text in the browser window are rendered with ClearType.

Actual result

Text in the address bar and bookmarks toolbar items are rendered without ClearType.
Text of tab labels, sidebar header, and the "Import bookmarks..." item are still rendered with ClearType, on my environment.

Comment 1

[YUKI "Piro" Hiroshi]

Attachment: Screenshot of enabled/disabled ClearType

Comment 2

[YUKI "Piro" Hiroshi]

I've confirmed this on Nightly 123.0a1 (build ID: 20240116050321) on Windows 11 23H2.
Here is another report on Firefox 120.0 on Windows 10 22H2: https://github.com/piroor/treestyletab/issues/3416

Comment 3

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

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

For more information, please visit BugBot documentation.

Comment 4

[Glenn Watson [:gw]]

This is a known / general issue. There's typically two underlying reasons we lose subpixel AA. First is if we fall back to blob rendering for an element, which doesn't support subpixel AA. Second is if we don't detect the correct conditions for an opaque background (we're somewhat conservative here to avoid artifacts) we disable subpixel AA. Each case requires individual investigation to see what's causing it.