Troj/JSDl-A is a downloading Trojan.
The Trojan collects information about the browser being used and the level of patching that has been applied.
Depending on the information collected a request is made ( a redirect ) for a remote script that delivers exploit code. If the browser in question is Microsoft Internet Explorer on a Windows platform the Trojan chooses between the (MS03-011) and (MS06-014) vulnerabilities. If the browser is a version of Mozilla Firefox then the Trojan attempts the (MFSA 2005:50) or (MS06-006) vulnerabilities.