I was able to reproduce the problem and found the following steps helped to resolve it for me:
follow step 12 of the adobe troubleshooting guide to recreate the users configuration folder:
after renaming the configuration folder, make sure to open Dreamweaver, then close it again.
only after opening it once, start the extension manager and reinstall the extensions.
Looks like Dreamweaver needs to be started to create the menu file, then you can install the extensions to have them added to the menu file.