Bug 1189212 for FX removed the tab images and uses the ::before selector to add a 1px wide line. This bug is to follow FX.
Created attachment 8665012 [details] [diff] [review] tab-separator.patch This is more or less a copy of the FX changes. I also added the follow bugs bug 1201442 and bug 1207164. I tested it on WinXP - 10 and Linux. This should also work on OS X like with FX.