1. Clone
OpenJFX 8.
$ openjfx% hg clone http://hg.openjdk.java.net/openjfx/8/graphics/rt
$ openjfx% cd rt
2. Checkout a tag for your JDK.
$ openjfx/rt% java -version 2>&1 | grep "build 1.8"
Java(TM) SE Runtime Environment (build 1.8.0-ea-b111)
$ openjfx/rt% hg checkout 8.0-b111
3. Set properties for Mavericks.
$ openjfx/rt% cat gradle.properties
MACOSX_MIN_VERSION=10.9
MACOSX_JDK_FRAMEWORK=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/System/Library/Frameworks/JavaVM.framework
4. Build jfxrt.jar.
$ openjfx/rt% gradle jfxrtMac
5. (If you want to use OpenJFX as default) Replace the bundled jar with the jar you built.
$ openjfx/rt% sudo mv $JAVA_HOME/jre/lib/ext/jfxrt.jar $JAVA_HOME/jre/lib/ext/jfxrt.jar.orig
$ openjfx/rt% sudo cp build/mac-sdk/rt/lib/ext/jfxrt.jar $JAVA_HOME/jre/lib/ext/jfxrt.jar
That's it. Enjoy the open source JavaFX ;)