Windows – Firefox 1.0.7 & 1.5.0.6, Internet Explorer 5.01, 5.5, 6 & 7b2, Mozilla 1.7.12, Netscape 7.2, Opera 8.5.4 & 9.01;
Mac – Camino 1.0, Firefox 1.0, 1.5 & 2.0b1*, Internet Explorer 5.2.3 (OSX) & 5.1.7 (OS9), Mozilla 1.7.12, Netscape 7.2, Opera 8.5.0, Safari 1.2, 1.3 & 2.0;
Linux – Firefox 1.5.0, Konqueror 3.4.0, Mozilla 1.7.12, Opera 9.
* Tested using I don't have a Mac myself and if anyone knows how to enable tabbing between links in Firefox for the Mac, I'd like to hear from you. ;)