This helps diagnose problems with web browser motion fluidity. Wait until the graph fills up, and then take a screen shot of this web page.
W3C Recommendation www.w3.org/TR/animation-timing/, end of section 5, recommends HTML5 animations to be synchronized to refresh rate.
See compliant browsers. Web browsers are extremely sensitive to stutters, so some manual optimization will help:

• IMPORTANT: Close all applications & close all other browser tabs;
• Close all RGB system tray software & other inefficient background software;
• Close all CPU Monitors & Task Manager. They sometimes creates a red spike every second;
• Use primary monitor only, or use single monitor mode instead of multimonitor.
• Use "High performance" power plan if using a laptop, and select your highest performance GPU;
• If using Safari, turn off "Prefer Page Rendering Updates near 60fps". See supported refresh rates;
• Refresh TestUFO if running for long time. Use Ctrl+R keypress or restart the browser;
• For 360Hz+ convention demos stuttering after 5 minutes, use automatic refresh (&kiosk=1 in URL);
• Verify GPU acceleration is working. Verify chrome://gpu. Also, some renderers was buggy (e.g. Vulkan in 2023).

Visual Frame Skipping Indicator: If you enable this indicator, you can visually watch for skipped frames to see if skipped frames co-relate with spikes. Successful browser frameskip self-detection is usually only relatively reliable with certain compositors (e.g. Windows + Primary Monitor). When a frameskip occurs, you will see erratic magenta/cyan color flicker instead of a steady flicker (at low Hz) or steady color (at high Hz). Alternatively, use the separate Frame Skipping test too.
NOTE: The Visual Frame Skipping Indicator should not be used by flicker-sensitive individuals.