The Appple Developer Team has given us now detailed information why the app was rejected: the safe browsing may not load all content of a web page and the App Review Team found that this may result in "incorrect" rendering/displaying of web pages.
We now made the "safe browsing" optionally - this way the user can decide whether to browse safely or not (and to accept "incorrect" rendering or not).
For those who do not understand the reason for safe surfing: a lot of web sides load data from other providers and thereby give user data to these providers. By browsing (now optionally) safely only content from the web side is loaded (and thereby the user can avoid to give data to other providers).
Another effect is to avoid redirections to mobile web sides - which sometimes is helpful if one wants to use the "normal" web content.