Browser is forwarded to internal URL of MS Dynamics CRM server

I think you're running into the issue detailed on page 10 of the guide. The internal server doesn't know it's behind a proxy, so it's sending absolute links to its known host name. A STREAM profile should solve that problem:

If your Dynamics CRM user interface is not correctly displaying page objects located in the /help directory, you may need to configure a Stream profile on the BIG-IP system to ensure the correct FQDN for your Dynamics deployment is returned to the client browser. The stream profile Target field should be comprised of one or more pairs of values, separated by the @ symbol. The first value corresponds to the NetBIOS name of a server in your deployment, and the second value is the fully qualified domain name (FQDN) that clients use to access Dynamics CRM. For example, if you have two servers in your Dynamics 2011 CRM deployment named server01 and server02, and the FQDN of the deployment is dynamics.mycompany.com, the Stream profile Target field would be:

@internalnameofcrmserver.internaldomain.local@crm.publicdomain.de@