Chrome and IE 11 are fine, I'm only able to reproduce this in Firefox. Using version 27.0.1 on Windows 7. Meta as well as all the other sites are affected.
I can still see the hover effect, but the image is gone. I see this in Firebug:
The image doesn't show up in the Network tab. I am able to see the image by visiting https://meta.stackoverflow.com/content/stackoverflowmeta/../img/share-sprite-new.png?v=204b1e0e421b which goes to https://meta.stackoverflow.com/content/img/share-sprite-new.png?v=204b1e0e421b
I've done Ctrl-F5, I've cleared the cache and I've tried Private Browsing. Possibly related to Stack Exchange™ MultiCollider SuperDropdown™ image wacked ?