It seems that adding the steps "Browser settings - Clear cache" and "Browser settings - Clear cookies" at the beginning of a project is not necessary and cache and cookies are deleted automatically when project (re-)starts.
Added a small sample project that opens to webservices. One sets and checks a cookie and the other write some data to the cache and read it when you go to the webpage again. Both sites show that cache and cookies are cleaned when a project is restarted.