I have had a similar problem with both web browsers (Firefox 3.5.3; Safari 4.0.3). The Silverlight download page does not allow one to choose which version (1, 2 or 3) to download. One would have to download, say version 3, with the appropriate OS/web browser, and then copy the plugin and paste it into one's Mac. However, I was successful in getting onto freestockcharts.com using my old desktop PC (Windows XP professional), which uses version 3 of the Silverlight plugin.
Here is the HELP email that you might find to be of assistance: <Feedback@FreeStockCharts.com>. Good Luck!