Problem is uncovered by latest JRE imports update. You can see it if you install .dmg from latest 2.2 Master build and
same problem will be in the 7u6 master.

All webstart apps on Mac stuck with splash screen visible and following stack:

"main" prio=5 tid=0x00007fd091800800 nid=0x1c03 runnable [0x000000011022a000]
   java.lang.Thread.State: RUNNABLE
    at com.sun.glass.ui.mac.MacApplication._runLoop(Native Method)
    at com.sun.glass.ui.mac.MacApplication.runLoop(MacApplication.java:56)
    at com.sun.glass.ui.Application.run(Application.java:124)
    at com.sun.glass.ui.Application.Run(Application.java:119)
    at com.sun.javafx.tk.quantum.QuantumToolkit.startup(QuantumToolkit.java:271)
    at com.sun.javafx.application.PlatformImpl.startup(PlatformImpl.java:122)
    at com.sun.deploy.uitoolkit.impl.fx.FXPluginToolkit.doInitIfNeeded(FXPluginToolkit.java:105)
    - locked <0x00000007e43dcc68> (a java.lang.Object)
    at com.sun.deploy.uitoolkit.impl.fx.FXPluginToolkit.warmup(FXPluginToolkit.java:168)
    at com.sun.javaws.Main.main(Unknown Source)


====== Original SQE report:
Issue found with mac nightly build 474, on mac 10.7.3 with both FF/Safari.
http://rehudson.us.oracle.com:8080/hudson/job/jdk-2-build-mac-universal-deploy/474/
Install the build and open any fx testcases which load fx apps through jnlp, like:
http://sqeweb.us.oracle.com/net/sqenfs-1/export1/comp/jsn/users/larry/fxfeaturesTest_dt187/html/testDocumentbase_JNLP.html
The dtjava.js is generated with latest ant lib from: http://jfx.us.oracle.com/hudson/view/2.2/job/2.2/label=macosx-universal-14/lastSuccessfulBuild/artifact/artifacts/sdk/lib/ant-javafx.jar
This looks like dt issue, as using cases generated with older version of antjavafx.jar, the same page can load fine:
http://sqeweb.us.oracle.com/net/sqenfs-1/export1/comp/jsn/users/larry/fxcases/fxfeaturesTest/html/testDocumentbase_JNLP.html