-webkit-gradient is parsed as URL resource.

[hrj]

A css rule such as:

background-image: -webkit-gradient(
     linear,
     left bottom,
     left top,
     color-stop(0.2, rgba(94, 94, 94, 0.5)),
     color-stop(0.9, rgba(24,24,24, 0.1))
   );

gets parsed as if a URL was specified for the background image. It causes the user agent to start fetching this URL:

http://blahblah/-webkit-gradient(linear, left bottom, left top, color-stop(0.2, rgba(94, 94, 94, 0.5)), color-stop(0.9, rgba(24,24,24, 0.1)));

[hrj]

Btw, when the standard variant (linear-gradient) is provided, it works fine.

But not all sites have switched to the standard yet.