Some Oracle JDeveloper 126.96.36.199.0 customers on the Mac OSX platform have reported a recurring deadlock (hang or more commonly known as a beachball on OSX) when switching between the JSF/JSPX visual editor and source editor and back again. Oracle engineering has investigated and discovered that most if not all of these deadlocks occur due to interference from 3rd party OSX windows management software, that is software that allows users to manipulate the layout of the OSX windows beyond the default OSX behaviour. This software to install and override the OSX default window behaviour typically installs itself though the OSX accessibility API. The API is designed to support applications assisting users with disabilities, but can also be utilized by applications willing to change how the OSX windows manager works.
You can discover the list of applications that have done this by opening the Mac System Preferences (via the Apple menu) > Security & Privacy option > Privacy tab > Accessibility options, as can be seen in the following picture:
The current workaround for this JDeveloper release is to disable the 3rd party OSX windows management software extensions through the OSX options described above (you'll need to unlock the dialog by entering your administrator password after clicking the padlock). This change should not need to apply to “real” accessibility extensions such as screen readers.