[css-content] Inserting and replacing content with the 'content' property

Since Dave started a thread on de-outofdatifying CSS Generated Content Module L3 - we've found a recent related interoperability issue I wanted to discuss.

We've got reports that Google Glass website [1] doesn't show GLASS logo on IE/Firefox, but does show it on Chrome. Investigation showed that actual image is inserted as content of an <a> element [2].

To my understanding this is spec'd in css-content spec [3], and as far as I can understand this was implemented in WebKit at some point. However it's not really clear what's the expected behavior here - pseudo elements address many questions on actual content insertion and are supported more universally.

This is currently the only instance of such behavior - but we would be interested in CSS WG opinion on the topic. Is content for arbitrary elements expected behavior for current specs?

[1] https://developers.google.com/glass/
[2] http://jsfiddle.net/0vcj32nz/1/
[3] http://www.w3.org/TR/css3-content/#inserting3