Created attachment 134875 [details]
In the attached example, the <h1> ("Page Title") tag is graphics-accelerated ("-webkit-transform: transform3d(0,0,0)"). The dialog <div> overlaps the <h1> tag (made visible with an semi-transparent background). The text inside the <h2> tag (which is inside the dialog <div>) does not have any sub-pixel font smoothing.
Adding a background-color to the <h2> tag will enable sub-pixel antialiasing again. It seems this shouldn't be necessary since the "dialog-content" <div> already has an opaque background color.
Changing the "top: 5%" to "top: 15%" (maybe higher, depending on window size...) on the "dialog" <div> will also re-enable sub-pixel antialiasing (since that div will no longer overlay the graphics-accelerated <h1> tag.
Seeing this in Safari on Mac OS X Snow Leopard [Version 5.1.4 (6534.54.16)], Chrome on Mac OS X Snow Leopard [17.0.963.83], Chrome on Windows 7 [18.0.1025.142 m].
*** This bug has been marked as a duplicate of bug 23364 ***