Silverlight 5 is the only version currently supported*. Silverlight 5 will support the browsers listed on this page through October 12, 2021, or through the lifecycle of the underlying browsers, whichever is shorter. Go here to learn more. Paid technical help is available to customers requiring support with issues beyond install and upgrade. Microsoft will continue to ship updates to the Silverlight 5 runtime for existing browser versions given that their extensibility model supports plug-ins, including updates for security vulnerabilities as determined by the Microsoft Security Response Center (MSRC).
Go here to learn more.
*Silverlight will reach the end of support on October 12, 2021. There is no longer support for Chrome, Firefox, or any browser using the Mac operating system.