Hmm, the fact that it's border radius dependent suggests this may be because of  issue 567296 . However, I feel like we'd expect to see lots of repainting if that was the case.

This is most likely due to the composited transform: scale() animation and would be decided by paint whether the image gets rasterised to avoid blurriness.

Tien-Ren/Xianda, do you have any idea why this is happening? I think the only difference between border-radius and not is a composited mask. Is there a rounding
bug in there?

Currently mask tiling is not enabled. It seems the issue still persists even if we do not composite anything by removing all will-change:transform (I see no cc layers in devtools, but I'm unsure about this, correct me if I'm wrong). Also only removing the border-radius property of the .expando element does not make the blur go away. Still thinking...

Looks like the problem only happens with gl_renderer, and it's related to render surface as it persists if I replace border-radius with opacity:0.99.

I think it's related to how gl_renderer draws RPDQ with scale transforms. I made a minimal case https://jsfiddle.net/txh7zqqw/.

The two scale factors: 8.123424141 * 0.1231007987 = 1.

Even in stable it's blurry. And I believe when you adjust the scale factor, the blurred text can look crisp if the scale factor is some certain magic value. And this causes the flickering animation.

In the class 

   .expando__inner

Remove the property

   overflow: hidden;

Then the text is no longer blurry.