Safari 9 support "pinned tabs", and Apple introduced a new meta-header to specify the image that should be used there: <link rel="mask-icon" href="website_icon.svg" color="red"> Without the meta tag it picks a letter from the text/title of the page (for some reason, it chooses "A" on my install):

Phabricator should serve that meta tag, and add a .svg file to the favicons folder.

Documentation: https://developer.apple.com/library/prerelease/ios/documentation/AppleApplications/Reference/SafariWebContent/pinnedTabs/pinnedTabs.html
Blog post on implementing it: http://blog.iconfactory.com/2015/11/the-new-favicon/