http://bugs.winehq.org/show_bug.cgi?id=27649
--- Comment #4 from Rosanne DiMesio dimesio@earthlink.net 2012-02-03 21:32:52 CST --- Silverlight 4 will no longer install in 1.4-rc2, not even with the workaround in bug 18345.
Silverlight 5 is the version currently available for download, and it does install, though the automatic update at the end fails. Tested with Firefox 5 (and the workaround for bug 17273), the page at http://bubblemark.com/silverlight2.html no longer shows the prompt to download Silverlight, and does try to load the animation, but fails.