I went through all of those problems myself and just figured out what works by first renaming my entire configuration folder and starting over.
I found that after trial and error (at least on the Mac), that certain extensions have to be installed in a precise order.
So, to fix my woes, here's what I found:
First, install Form Toolkit.
Second, install Form Builder 2.0.1 beta.
Third, install HTML Editor 3.0.2.
After you confirm it works, I would recommend making a duplicate of your configuration folder and that way when if you install something else that were to break the functionality, you can always revert back to the configuration where you know it last worked.