Whole UI becomes blurry/fuzzy when hardware acceleration is enabled

[Eadams8]

Environment

• Zen Browser 1.21.15b (Firefox 154 base)
• OS: Windows
• GPU: NVIDIA GeForce RTX 2070 SUPER (driver up to date, July 2026 build)
• Display: 4K (3840x2160) @ 100% scaling
• Hardware acceleration: enabled

Description

With the Animations Plus mod installed and hardware acceleration enabled, the entire
browser UI becomes blurry/fuzzy — fonts, icons, toolbar buttons, even the window close
button. The blur is transient and pulses: it often triggers when hovering over elements
and clears again after a moment. It also appears when window focus changes.

With hardware acceleration disabled everything is sharp, and stock Firefox with hardware
acceleration enabled renders perfectly sharp on the same machine — so the issue appears
to be an interaction between this mod's CSS transitions and WebRender compositing.

Steps to reproduce

1. Install Animations Plus mod, keep hardware acceleration enabled
2. Hover over tabs / toolbar buttons, or switch window focus
3. Observe UI-wide blurriness that fades in and out

Isolation performed

• Disabling the mod completely fixes the issue ✔
• gfx.webrender.all, ClearType params (gfx.font_rendering.cleartype_params.*), and
  zen.view.experimental-rounded-view were tested in all combinations — none had any effect
• No other gfx overrides active; clean profile behavior identical

Expected result

UI stays sharp during hover transitions with GPU acceleration on.