1924360 - Incorrect Target Frame Rate in about:support using HRR on Wayland

Status: UNCONFIRMED

(Core :: Widget: Gtk, defect, P3)

Description

[James Heppell [:FormularSumo]]

User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:131.0) Gecko/20100101 Firefox/131.0

Steps to reproduce:

Run the latest version of Firefox on Wayland on a high refresh rate (>60) display, and enable high refresh rate on the OS.

Actual results:

Firefox correctly matches the display/OS frame rate of in my case 90 hz. This can be checked for example on this page https://www.testufo.com/framerates-versus#photo=dota2-bg.jpg&pps=1920&framepacingerror=0.1&direction=rtl&framerate=60&compare=2&showfps=1&kiosk=1 which reports the browser's FPS and shows a visual comparison between its full frame rate and 60 FPS. There's a noticeable difference between the two on both Firefox and Chromium browsers when the OS is set to 90hz, but no difference when the OS is set to 60hz.

However, despite correctly matching the OS/display frame rate, Firefox on Wayland reports the target frame rate as 60 in about:support. If I manually change layout.frame_rate in about:config to be another value such as 90 or 40, the target frame rate is updated in about:support, but the actual frame rate of Firefox remains unchanged (again using the previous example). This remains the case even if I set widget.wayland.vsync.enabled to false*.

When running Firefox on X11, about:support does correctly report a target frame rate of 90 with layout.frame_rate set to its default value of -1.

*See https://bugzilla.mozilla.org/show_bug.cgi?id=1771017

Expected results:

Firefox on Wayland correctly reports the target frame rate in about:support to avoid confusion.