Just like Flex requires flash player to run in browser, JavaFX would run in the browser as an
applet.
Also JavaFX supports Webkit browser engine which enables one to render html pages within a javafx application.
I think JavaFX has no greater learning curve, but may be you would have to get familiar with the apis added as part of JavaFX.
Being familiar with
Java would be a plus.
JavaFX application would require javafx runtime to be installed.