FireFox 3.0 has still the memory leak woes, take look at the memory consumption for firefox with only four tabs opened for more than 15 hours.
The System.Web.VirtualPathUtility class has some very useful method for converting from an app relative path to an absolute path:
string absoluteUrl = VirtualPathUtility.ToAbsolute(relativeUrl);
Here is the solution
Open IE7 > Tools > Internet Options
Click on the "Programs" tab
Click on the "Set Programs" button
Click the "Set program access and computer defaults" link
Click the "Custom" option
Go down to the "Choose a default media player:" option and select "Windows Media Player"
Click the "Ok" button
Close "Default Programs" window
Click the "Ok" button on the "Internet Options" window